7.2 Exterior Angle Theorem
You will learn to identify exterior angles and remote interior angles of a triangle and use the Exterior Angle Theorem. 1) Interior angle 2) Exterior angle 3) Remote interior angle
P QR In the triangle below, recall that 1, 2, and 3 are _______ angles of ΔPQR. interior Angle 4 is called an _______ angle of ΔPQR. exterior An exterior angle of a triangle is an angle that forms a _________ with one of the angles of the triangle. linear pair In ΔPQR, 4 is an exterior angle at R because it forms a linear pair with 3. ____________________ of a triangle are the two angles that do not form a linear pair with the exterior angle. Remote interior angles In ΔPQR, 1, and 2 are the remote interior angles with respect to 4.
In the figure below, 2 and 3 are remote interior angles with respect to what angle? 55
Theorem 7 – 3 Exterior Angle Theorem The measure of an exterior angle of a triangle is equal to sum of the measures of its ___________________. remote interior angles X ZY m 4 =m 1 + m 2
Theorem 7 – 4 Exterior Angle Inequality Theorem The measure of an exterior angle of a triangle is greater than the measures of either of its two ____________________. remote interior angles X ZY m 4 >m1m1 m2m2
1 and 3 74° 13 2 Name two angles in the triangle below that have measures less than 74°. Theorem 7 – 5 If a triangle has one right angle, then the other two angles must be _____. acute
The feather–shaped leaf is called a pinnatifid. In the figure, does x = y? Explain. x = y ? __ + 81 = ° 109 = 110 No! x does not equal y