Are You Ready? Find Perimeter

Transcription

1 SKILL 3 Find Perimeter Teaching Skill 3 Objective Find the perimeter of figures. Instruct students to read the definition at the top of the page. Stress that the shape of the figure does not matter the method for finding the perimeter will be the same: add the lengths of all the sides. Ask: What is true about a regular figure? (All the sides of a regular figure are equal.) What is true about the sides of a rectangle or a parallelogram? (Opposite sides are equal.) What is true about the sides of an isosceles triangle or an isosceles trapezoid? (The two sides that are not parallel are equal.) Point out that when working with figures that have equal sides, it is a good idea to label all the sides. This will remind students to add all of the sides to correctl find the perimeter. Instruct students to work through the eample, step b step. Remind them to alwas include units when given. PRACTICE ON YOUR OWN In eercises 1, students find the perimeter of the given figure. CHECK Determine that students know how to find the perimeter of various figures. Students who successfull complete the and are read to move on to the net skill. Alternative Teaching Strateg Objective Find the perimeter of figures. Materials needed: a ruler, a ardstick and a fleible measuring tape Have the students measure the length and width of their math tetbook. Then have them sketch a diagram of the book on a piece of paper and label the sides according to the measurements the took. Remind students that perimeter is equal to the distance around a figure. Have the students use a fleible tape measure to measure around the entire book and record their answer. Net, instruct the students to use the formula for finding perimeter to confirm their answer: P s 1 s s 3 s Repeat the eercise b having the students measure the sides of their desktop and find the perimeter using both the tape measure and the addition formula. Ask: Can ou find the perimeter of triangles using the same method? (Yes) How about pentagons or heagons? (Yes) And circles? (No) Wh not? (A circle does not have sides that ou can add up.) Instruct students to choose other objects in the room to practice measuring, sketching, and finding perimeter. Have the students compare their answers with other students who measured the same objects. COMMON ERRORS Students ma not include all sides when finding the perimeter of a figure. Students who made more than 1 error in the, or who were not successful in the section, ma benefit from the Alternative Teaching Strateg. 83 Holt McDougal Geometr

2 Name Date Class SKILL 3 Find Perimeter Definition: The perimeter of a figure is the distance around the figure. The shape of the figure is not important. To find the perimeter of an figure: Step 1: Label all the sides with the correct lengths. Step : Write an equation: P s 1 s s 3 Step 3: Find P b adding the values. Don t forget to include units. Eample: Find the perimeter of the regular pentagon. cm cm cm cm cm cm Find the perimeter of each figure. P = P = 10 cm 1. triangle ABC. square DEFG 3. regular octagon MNPQRSTU P P P. parallelogram WXYZ 5. pentagon DEFGH. isosceles triangle LMN P P P Find the perimeter of each figure. 7. equilateral triangle RST 8. heagon EFGHJK 9. isosceles trapezoid ABCD P P P 8 Holt McDougal Geometr

3 SKILL 35 Find Missing Measures in Similar Figures Teaching Skill 35 Objective Find missing measures in similar figures. Instruct students to read the statement at the top of the page and the similarit proportion statements. Remind students that a proportion is a statement that two ratios are equal. Emphasize that the order in which the proportion is written depends on the order of the letters in the figure names. Have students look at the eample and consider the sides of the figures that are given and the side that is missing. Point out that H and J are the first two letters in the name of the figure and H and L are the first and last letters. Ask: Which letters are P and S? (first and last) And the missing side, PQ? (first and second) Stress that this matters when setting up the proportion. Write on the board: first two first and last first two first and last Encourage students to write proportions using this method. PRACTICE ON YOUR OWN In eercises 1 7, students determine which sides and angles of similar figures can be found, and find the missing measures. CHECK Determine that students know how to find the missing measure in similar figures. Students who successfull complete the and are read to move on to the net skill. COMMON ERRORS Students ma not pa attention to the order of the letters in figure names and ma mismatch sides or angles. Students who made more than errors in the, or who were not successful in the section, ma benefit from the Alternative Teaching Strateg. Alternative Teaching Strateg Objective Find missing measures in similar figures. Draw the triangles shown below on the board. One triangle should be about 3 times the size of the other. Have the students draw approimatel the same triangles on their paper. 81 Holt McDougal Geometr Net, write the following statement on the board in large letters: ABC DEF Ask: According to the diagram, which angle of triangle DEF corresponds to angle ABC? (DEF ) Ask: If the measure of angle ABC is 0, what is the measure of angle DEF? (0) Repeat the question for each of the angles. Point out that the letters of corresponding angles are written in the same order as in the names of the triangles. Have students label the diagram as follows: AB, BC 5, EF 15, and DE? Ask: According to the diagram, which side corresponds to AB? (DE ) Which side corresponds to BC? (EF ) Again, point out the relevance of the order in which the letters are written in the names of the triangles. Review with students how to set up and solve a proportion. Have students set up the following proportion. Then substitute appropriate values and solve. AB BC DE EF 5? 15, DE Repeat this eercise using diagrams of similar rectangles. Be sure to emphasize the order of the letters each time.

4 Name Date Class SKILL 35 Find Missing Measures in Similar Figures Corresponding sides of similar polgons are proportional. Corresponding angles of similar polgons are congruent. Notation: ABC DEF Remember: order matters! Similarit proportion statements: AB DE BC EF ; AC DF BC EF ; AB AC DE DF ; etc. Eample: HJKL PQRS. HJ, HL, and PS 7. What is PQ? Step 1: Write a proportion using letters; use the sides given and the missing side: HJ PQ HL PS Step : Replace the given sides with the appropriate values: PQ 7. Step 3: Solve the proportion using cross-multiplication: (7) (PQ); PQ (7) 1 1. RST XYZ. Complete the congruence statement: mtsr m. ABC STU. mbca. What other angle has a measure of? 3. AGPS DHNZ. mgps 5 and mpsa 115. What is the measure of NZD?. DEFG LMNO. If ou know the values of DE, DF, and LN, for which other side is it possible to find the length? 5. ABCDE LMNOP. Complete the proportion: BE AC LN. HPV UBK. UB 18, HP, and BK 90. What is PV? 7. WXYZ PQRS. XY 5, YZ 1, and QR 30. What is RS? 8. FGH LMN. mhfg 8. What other angle has a measure of 8? 9. ABCD PQRS. mabc 80 and mdab 100. What is the measure of PQR? 10. JKLM DEFG. If ou know the values of DF, DG, and JL, for which other side is it possible to find the length? 11. CDE HJK. DE, JK 3, and CE. What is HK? 1. UVWX CDEF. WX 9, VW 11, and EF 3. What is DE? 8 Holt McDougal Geometr

5 SKILL 3 Special Right Triangles Teaching Skill 3 Objective Find the length of a side of a special right triangle. Review with students the properties and the diagrams of the special right triangles. Point out that for a triangle, if the length of either leg is given, then finding the lengths of the other leg and the hpotenuse is eas. However, if the hpotenuse is given (and does not have a in it), then finding the lengths of the two legs is not as eas. Stress that students will need to set up and solve an equation. Work an eample like problem 7 to demonstrate how to do this. Approach triangles the same wa. Point out that if the shorter leg or the hpotenuse is given, the calculations are eas; if the longer leg is given (and does not have a 3 in it), students will need to use an equation. Work an eample to demonstrate. PRACTICE ON YOUR OWN In eercises 1 8, students use properties of and triangles to find the length of an unknown side of the triangle. CHECK Determine that students know how to use special right triangle properties to find the length of a side. Students who successfull complete the and are read to move on to the net skill. COMMON ERRORS Students ma confuse the order in which the 1 : 3 : ratio applies to the sides of a triangle. Students who made more than errors in the, or who were not successful in the section, ma benefit from the Alternative Teaching Strateg. Alternative Teaching Strateg Objective Verif the ratios of the sides of special right triangles. Materials needed: two pieces of lined paper, a ruler, and a protractor Draw a triangle on the board. Remind students that the two legs should be equal and the hpotenuse should be times the lengths of the legs. Have students take one piece of lined paper and fold it carefull in half (verticall), making a distinct crease in the paper. Instruct them to unfold the paper. Instruct students to use a ruler to do the following: 1) Draw a -inch line along the crease, beginning at an line near the bottom of the sheet of paper. ) At the bottom of the line the drew, draw a horizontal line that is inches long. 3) Connect the two lines with a diagonal, forming a right triangle. Ask: Since the two legs are equal ( inches), what should the measure of the two smaller angles be? (5) Have students use protractors to verif this. Net, tell students that is approimatel equal to 1.. Have the students use their ruler to measure the length of the hpotenuse. Ask: Is the length of the hpotenuse approimatel 1.? (It should be.) Net, have students fold the other piece of paper in the same wa, forming a crease. Remind students of the properties of a triangle. Tell students that 3 is approimatel equal to Have students draw a horizontal line near the bottom of the page that is 3 inches long and vertical line up the crease that is or 5.5 inches long. Instruct students to use a protractor to measure the angles of the triangle and a ruler to measure the length of the hpotenuse. (The angles should be roughl 30 and 0 and the hpotenuse inches.) 75 Holt McDougal Geometr

6 Name Date Class SKILL 3 Special Right Triangles Triangles 1. Both legs are congruent.. The length of the hpotenuse is times the length of a leg Triangles 1. The length of the hpotenuse is twice the length of the shorter leg.. The length of the longer leg is 3 times the length of the shorter leg. s s 30 s 3 s s s Eample: Find the value of. Give the answer in simplest radical form. Answer: In a triangle, the length of the hpotenuse is twice the length of the shorter leg. So solve: (5) or 10. Find the value of. Give the answer in simplest radical form Find the value of Holt McDougal Geometr

7 Name Date Class CHAPTER 11 Enrichment Finish It Off The area of each figure is given. Plot the given points and then find the missing coordinate(s) for each figure. Note: the missing coordinate is alwas positive. 1. The area of parallelogram ABCD is 8 square units. A (3, 1) B (, 1) C (, ) D (9, ) 8. The area of triangle EFG is 1 square units. E (, ) F (5, ) G (1, ) 3. The area of circle P is 5 square units. The center of the circle is (1, 3) and the circle passes through the point (, 3). The area of trapezoid HJKL is square units. H (, ) J (, ) K (5, ) L (, ) 5. The area of right triangle MNP is 7 square units. M (3, ) N (3, ) P (3, ) 05 Holt McDougal Geometr

8 Answer Ke continued 7. A and C 8. Yes; corresponding sides are in proportion (1:.5) 9. Yes; corresponding sides are in proportion (1:3) SKILL 35 ANSWERS: 1. ZYX. TUS LM 5. MP NLM JM SKILL 3 ANSWERS: in.. 5 cm 3. 8 in.. m ft. 1 in in ft 9. 3 cm SKILL 37 ANSWERS: in.. 1 ft 3. 1 cm. m ft. 35 d 7. 9 in. 8. m cm 10. m ft 1. 0 in. SKILL 38 ANSWERS: 1. 3 units. 0 units units units 5. 0 units. 9 units units 8. 1 units units units units 1. 9 units 19 Holt McDougal Geometr

9 Answer Ke continued SKILL 30 ANSWERS: SKILL 31 ANSWERS: SKILL 3 ANSWERS: SKILL 33 ANSWERS: 1. Yes; ASA. No 3. Yes; HL. Yes; ASA 5. Yes; SAS. No 7. No 8. Yes; HL 9. Yes; SSS SKILL 3 ANSWERS: 1. A and D. B and C 3. Yes; corresponding sides are in proportion (1:). Yes; corresponding sides are in proportion (7:1) 5. Yes; corresponding sides are in proportion (:1). No 18 Holt McDougal Geometr