EXPLANATION
If the measure of ∠2= x+78 and the other ∠=40 degrees, by definition we know that sum of interior angles of a triangle is equal to 180 degrees.
Furthermore, we have two congruent legs, so this is an Isosceles triangle with two congruent angles (with the same measure).
Thus,
180 = 40 + 2* m∠2
Substituting m∠2 by the equation as follows:
180 = 40 + 2(x + 78)
Subtracting -40 to both sides:
180 - 40 = 2(x+78)
Simplifying:
140 = 2(x+78)
Dividing both sides by 2:
140/2 = x + 78
Simplifying:
70 = x + 78
Subtracting -78 to both sides:
70 - 78 = x
Simplifying:
-8 = x
Switching:
x = -8
Answer: The value of x is -8.
