Answer: x = 45
Work Shown:
x+x+90 = 180 .... all three angles of a triangle add to 180
2x+90 = 180
2x = 180-90
2x = 90
x = 90/2
x = 45
This is a 45-45-90 right triangle. We also consider it an isosceles right triangle because the base angles (45) are equal.