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4.1 Triangles & Angles

4.1 Triangles & Angles. August 15, 2013. 4.1 Classifying Triangles. Triangle – A figure formed when three noncollinear points are connected by segments. The sides are DE, EF, and DF . The vertices are D, E, and F. The angles are  D,  E,  F. Angle. E. Side. Vertex. F. D.

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4.1 Triangles & Angles

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  1. 4.1 Triangles & Angles August 15, 2013

  2. 4.1 Classifying Triangles Triangle – A figure formed when three noncollinear points are connected by segments. The sides are DE, EF, and DF. The vertices are D, E, and F. The angles are D,  E,  F. Angle E Side Vertex F D

  3. Triangles Classified by Angles Acute Obtuse Right 17º 50º 120º 60º 30° 70º 43º 60º All acute angles One obtuse angle One right angle

  4. Triangles Classified by Sides Isosceles Equilateral Scalene no sides congruent all sides congruent at least two sides congruent

  5. E C 60° 45° 60° 60° 45° B G A F Classify each triangle by its angles and by its sides.

  6. Fill in the table

  7. Try These: • ABC has angles that measure 110, 50, and 20. Classify the triangle by its angles. • RST has sides that measure 3 feet, 4 feet, and 5 feet. Classify the triangle by its sides.

  8. Adjacent Sides- share a vertex ex. The sides DE & EF are adjacent to E. Opposite Side- opposite the vertexex. DF is opposite E. E F D

  9. Parts of Isosceles Triangles The angle formed by the congruent sides is called the vertex angle. The two angles formed by the base and one of the congruent sides are called base angles. The congruent sides are called legs. leg leg base angle base angle The side opposite the vertex is the base.

  10. Base Angles Theorem If two sides of a triangle are congruent, then the angles opposite them are congruent. If , then

  11. Converse of Base Angles Theorem If two angles of a triangle are congruent, then the sides opposite them are congruent. If , then

  12. EXAMPLE 1 Apply the Base Angles Theorem Find the measures of the angles. SOLUTION Q P Since a triangle has 180°, 180 – 30 = 150° for the other two angles. Since the opposite sides are congruent, angles Q and P must be congruent. 150/2 = 75° each. (30)° R

  13. EXAMPLE 2 Apply the Base Angles Theorem Find the measures of the angles. Q P (48)° R

  14. EXAMPLE 3 Apply the Base Angles Theorem Find the measures of the angles. Q P (62)° R

  15. EXAMPLE 4 Apply the Base Angles Theorem Find the value of x. Then find the measure of each angle. P SOLUTION (12x+20)° Since there are two congruent sides, the angles opposite them must be congruent also. Therefore, 12x + 20 = 20x – 4 20 = 8x – 4 24 = 8x 3 = x (20x-4)° Q R Plugging back in, And since there must be 180 degrees in the triangle,

  16. EXAMPLE 5 Apply the Base Angles Theorem Find the value of x. Then find the measure of each angle. Q P (11x+8)° (5x+50)° R

  17. EXAMPLE 6 Apply the Base Angles Theorem Find the value of x. Then find the length of the labeled sides. SOLUTION Q P (80)° (80)° Since there are two congruent sides, the angles opposite them must be congruent also. Therefore, 7x = 3x + 40 4x = 40 x = 10 3x+40 7x Plugging back in, QR = 7(10)= 70 PR = 3(10) + 40 = 70 R

  18. EXAMPLE 7 Apply the Base Angles Theorem Find the value of x. Then find the length of the labeled sides. P (50)° 5x+3 (50)° R Q 10x – 2

  19. Right Triangles HYPOTENUSE LEG LEG

  20. Exterior Angles Interior Angles

  21. Triangle Sum Theorem The measures of the three interior angles in a triangle add up to be 180º. x + y + z = 180° x° y° z°

  22. R m R + m S + m T = 180º 54° 54º + 67º + m T = 180º 121º + m T = 180º 67° S T m T = 59º

  23. m  D + m DCE + m E = 180º E 55º + 85º + y = 180º B y° 140º + y = 180º C x° 85° y = 40º 55° D A

  24. Find the value of each variable. x° 43° x° 57° x = 50º

  25. Find the value of each variable. 55° 43° (6x – 7)° (40 + y)° 28° x = 22º y = 57º

  26. Find the value of each variable. 50° 53° x° 50° 62° x = 65º

  27. Exterior Angle Theorem The measure of the exterior angle is equal to the sum of two nonadjacent interior angles 1 m1+m2 =m3 2 3

  28. Ex. 1: Find x. B. A. 72 43 148 76 x x 38 81

  29. Homework: Practice WS

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