1.6 Angle Pair Relationships
Adjacent Angles Remember: Adjacent Angles share a vertex and a ray, but DO NOT share any interior points.
Which angle pairs are adjacent? <1&<2 <2&<3 <3&<4 <4&<1 Vertical Angles – 2 angles that share a common vertex & whose sides form 2 pairs of opposite rays. Vertical Angles are always congruent! <1&<3, <2&<4 Then what do we call <1&<3?
Linear Pair (of angles) 2 adjacent angles whose non-common sides are opposite rays. 1 2 Basically, it’s 2 adjacent angles that together make a straight line!
Example Vertical angles? <1 & <4 Adjacent angles? <1&<2, <2&<3, <3&<4, <4&<5, <5&<1 Linear pair? <5&<4, <1&<5 Adjacent angles not a linear pair? <1&<2, <2&<3, <3&<
Important Facts Vertical Angles are congruent. ALWAYS! THIS IS ONE ASSUMPTION YOU CAN ALWAYS MAKE! The sum of the measures of the angles in a linear pair is 180 o. REMEMBER: THE TWO ANGLES IN A LINEAR PAIR ARE Adjacent ANGLES THAT MAKE A STRAIGHT LINE!
Example: If m<5=130 o, find m<3 m<6 m< = 130 o =50 o
Example: Find x and y and m<ABE m<ABD m<DBC m<EBC 3x+5 o y+20 o x+15 o 4y-15 o x=40 y=35 m<ABE=125 o m<ABD=55 o m<DBC=125 o m<EBC=55 o A B C D E m<CBE + m<EBA = 180° Linear Pair x x + 5 = 180 Substitute 4x + 20 = 180 CLT 4x = 160 Subtraction x = 40 Division m<CBD + m<ABD = 180 Linear Pair 4y y + 20 = 180 Substitute 5y + 5 = 180 CLT 5y = 175 Subtraction POE y = 35 Division POE
Complementary Angles 2 angles whose sum is 90 o. The two angles DO NOT need to be adjacent! o A 55 o B <1 & <2 are complementary <A & <B are complementary
Supplementary Angles 2 angles whose sum is 180 o. Two angles can be supplementary and NOT BE A LINEAR PAIR o 50 o X Y <1 & <2 are supplementary. <X & <Y are supplementary.
Ex: <A & <B are supplementary. m<A is 5 times m<B. Find m<A & m<B. Let’s say m<A = 5b m<B = b
Angle A’s measure is 3 times its complement, <B. The measure of angle A’s supplement, <C, is 5 times m<B. Find the measures of all the angles. m<A + m<B = 90° 3b + b = 90 4b = 90 b = 22.5 m<A = 3*22.5= 67.5° m<C = 5b, so 5(22.5) = 112.5° Let’s say: m<B = b m<A = 3b m<C = 5b