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12. Right 32. 4 13. Obtuse 34. no; isos does not have the 3 = sides needed

12. Right 32. 4 13. Obtuse 34. no; isos does not have the 3 = sides needed 14. Equiangular yes; equilateral has the 2 = sides needed 15. Equilateral 39. see pictures 16. Isosceles 55. parallel 17. Scalene 56. perpendicular

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12. Right 32. 4 13. Obtuse 34. no; isos does not have the 3 = sides needed

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  1. 12. Right 32. 4 13. Obtuse 34. no; isos does not have the 3 = sides needed 14. Equiangular yes; equilateral has the 2 = sides needed 15. Equilateral 39. see pictures 16. Isosceles 55. parallel 17. Scalene 56. perpendicular 18. 8; 8; 8 57. coincides 19. 8.6; 8.6 58. perpendicular 21. 18 ft; 118 ft; 24 ft 22. 2 24. Not possible; must contain only acute angles 27. Not possible; must also be equilateral 30. isos., obtuse 31. isos, right

  2. Warm Up 1. Find the measure of exterior DBA of BCD, if mDBC = 30°, mC= 70°, and mD = 80°. 2. What is the complement of an angle with measure 17°? 3. How many lines can be drawn through N parallel to MP? Why? 150° 73° 1; Parallel Post.

  3. An auxiliary line is a line that is added to a figure to aid in a proof. An auxiliary line used in the Triangle Sum Theorem

  4. Example 1A: Sum. Thm After an accident, the positions of cars are measured by law enforcement to investigate the collision. Use the diagram drawn from the information collected to find mXYZ. mXYZ + mYZX + mZXY = 180° Substitute 40 for mYZX and 62 for mZXY. mXYZ + 40+ 62= 180 mXYZ + 102= 180 Simplify. mXYZ = 78° Subtract 102 from both sides.

  5. Example 1B: 118° Sum. Thm After an accident, the positions of cars are measured by law enforcement to investigate the collision. Use the diagram drawn from the information collected to find mYWZ. Step 1 Find mWXY. mYXZ + mWXY = 180° Lin. Pair Thm. and  Add. Post. 62 + mWXY = 180 Substitute 62 for mYXZ. mWXY = 118° Subtract 62 from both sides. Step 2 Find mYWZ. mYWX + mWXY + mXYW = 180° Substitute 118 for mWXY and 12 for mXYW. mYWX + 118+ 12= 180 mYWX + 130= 180 Simplify. Subtract 130 from both sides. mYWX = 50°

  6. A corollary is a theorem whose proof follows directly from another theorem. Here are two corollaries to the Triangle Sum Theorem.

  7. Acute s of rt. are comp. Acute s of rt. are comp. Example 2: One of the acute angles in a right triangle measures 2x°. What is the measure of the other acute angle? Let the acute angles be A and B, with mA = 2x°. mA + mB = 90° 2x+ mB = 90 Substitute 2x for mA. mB = (90 – 2x)° Subtract 2x from both sides. The measure of one of the acute angles in a right triangle is 63.7°. What is the measure of the other acute angle? mA + mB = 90° 63.7 + mB = 90 Substitute 63.7 for mA. mB = 26.3° Subtract 63.7 from both sides.

  8. The interior is the set of all points inside the figure. The exterior is the set of all points outside the figure. 3 is an interior angle. 4 is an exterior angle. Exterior Interior An interior angle is formed by two sides of a triangle. An exterior angle is formed by one side of the triangle and extension of an adjacent side.

  9. Each exterior angle has two remote interior angles. A remote interior angle is an interior angle that is not adjacent to the exterior angle. The remote interior angles of 4 are 1 and 2.

  10. Example 3: Applying the Exterior Angle Theorem Find mB. mA + mB = mBCD Ext.  Thm. Substitute 15 for mA, 2x + 3 for mB, and 5x – 60 for mBCD. 15 + 2x + 3= 5x – 60 2x + 18= 5x – 60 Simplify. Subtract 2x and add 60 to both sides. 78 = 3x 26 = x Divide by 3. mB = 2x + 3 = 2(26) + 3 = 55°

  11. Find mK and mJ. Example 4: K  J Third s Thm. mK = mJ Def. of s. 4y2= 6y2 – 40 Substitute 4y2 for mK and 6y2 – 40 for mJ. –2y2 = –40 Subtract 6y2 from both sides. y2 = 20 Divide both sides by -2. So mK = 4y2 = 4(20) = 80°. Since mJ = mK,mJ =80°.

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