Question

If ∠A and ∠B are supplementary angles and m∠B = (x + 20)°, then what would be m∠A?

Answer 1

Since ∠A and ∠B are supplementary angles.

∴ m∠A + m∠B = 180°

∴ m∠A + x + 20° = 180°

∴ m∠A + x + 20° − 20°= 180° − 20°           ...(Subtracting 20 from both sides)

∴ m∠A + x = 160°

∴ m∠A + x − x = 160 − x            ...(Subtracting x from both sides)

∴ m∠A + (160 − x)°

∴ The measure of ∠A is (160 − x​)°.