Solution:
We know that:
- Sum of interior angles of triangle: 180°
- Those 2 bars drawn on GH and IH defines that GH = IH.
This means that:
- The triangle is an isosceles triangle.
- The bottom two angles are equal.
Equation created: 58 + x + x = 180
Simplify the LHS.
- 58 + x + x = 180
- => 58 + 2x = 180
Subtract 58 both sides.
- 58 - 58 + 2x = 180 - 58
- => 2x = 122
- => x = 61
Thus, the measure of ∠GIH is 61°.