Angles Worksheets - Free Printable

To find the measure of the indicated exterior angle in each triangle, we use the Exterior Angle Theorem.

The Rule:
The measure of an exterior angle of a triangle is equal to the sum of the measures of its two remote interior angles.
*Formula:* Exterior Angle = Interior Angle 1 + Interior Angle 2

Let's solve each problem step-by-step:

a)
* Remote interior angles: $50^\circ$ and $80^\circ$
* Calculation: $50 + 80 = 130$
* $m\angle DBC = 130^\circ$

b)
* Remote interior angles: $45^\circ$ and $90^\circ$ (indicated by the square symbol)
* Calculation: $45 + 90 = 135$
* $m\angle EFG = 135^\circ$

c)
* Remote interior angles: $60^\circ$ and $70^\circ$
* Calculation: $60 + 70 = 130$
* $m\angle HJK = 130^\circ$

d)
* Remote interior angles: $30^\circ$ and $40^\circ$
* Calculation: $30 + 40 = 70$
* $m\angle MNO = 70^\circ$

e)
* Remote interior angles: $55^\circ$ and $65^\circ$
* Calculation: $55 + 65 = 120$
* $m\angle PQR = 120^\circ$

f)
* Remote interior angles: $45^\circ$ and $85^\circ$
* Calculation: $45 + 85 = 130$
* $m\angle WXY = 130^\circ$

g)
* Remote interior angles: $70^\circ$ and $40^\circ$
* Calculation: $70 + 40 = 110$
* $m\angle JKL = 110^\circ$

h)
* This is an isosceles triangle with base angles of $70^\circ$.
* Remote interior angles: $70^\circ$ and $70^\circ$
* Calculation: $70 + 70 = 140$
* $m\angle LMN = 140^\circ$

i)
* Remote interior angles: $50^\circ$ and $60^\circ$
* Calculation: $50 + 60 = 110$
* $m\angle STU = 110^\circ$

Final Answer:
a) 130°
b) 135°
c) 130°
d) 70°
e) 120°
f) 130°
g) 110°
h) 140°
i) 110°