How to Find the Missing Angle of a Triangle
A Few Main Points You Need to Know About Triangles
#1 All angles within a triangle must always add to 180°
#2 The small square in the corner of a triangle denotes a 90° angle
#3 Arcs denote that two angles are congruent (meaning they have the exact same measure)
#4 A straight lines always measures 180°
Finding the Measure of a Triangle when you have the other Two Measures
Remember that the Triangle will always add to 180°
Let's assume that the measure of angle A is 65º and the measure of angle B is 70°.
So we are looking for the measure of angle C
The sum of angles A + B = 65 +70 = 135
Since the sum of all the angles must be 180 we subtract the other two angles from it.
180 - (A+B) = C
180 - 135 = 55
The measure of angles C is 55°
Finding Measures of Triangles when a Straight Line in involved
Remember that a straight line is 180°
In triangle #2 we have one angle and need to find the other two angles.
The first thing we are going to do is find angle A. Since angle A is part of a straight line we can conclude the following equation.
A + 85 = 180
A + 85 -85 = 180 -85
A = 95°
Now we have two of the angles that are part of the triangle
95 + 40 + B = 180
135 + B = 180
B = 180 - 135
B = 45°