We know that An Isosceles Triangle has Two Equal Sides and Two Equal Angles Corresponding to those Two Equal Sides.
Given : WXY is an Isosceles Triangle :
From the Figure we can Notice that WY = XY
⇒ Angle (W) = Angle (X)
Given Angle (W) = (5x + 3)°
⇒ Angle (X) = (5x + 3)°
We know that Sum of Angles in a Triangle should be Equal to 180°
⇒ Angle (X) + Angle (Y) + Angle (W) = 180°
Given Angle (Y) = (11x - 15)°
⇒ (5x + 3)° + (11x - 15)° + (5x + 3)° = 180°
⇒ (21x - 9)° = 180°
⇒ 21x° = 189°
⇒ x° = 9°
⇒ Angle (Y) = (11x - 15)°
⇒ Angle (Y) = (11 × 9 - 15)° = (99 - 15)° = 84°
So the Measure of Angle (Y) = 84°
