HOTS Mathematics Primary 5 Geometry

Triangle XYZ is isosceles with XY = XZ. Ray XW bisects angle YXZ, where W lies on YZ. Angle WXZ = 40°. Find the sum of angle XWY and angle XZY.

A 90°
B 130°
C 140°
D 180°
Show Worked Solution

Worked Solution

Step 1: Find angle YXZ. XW bisects angle YXZ, and angle WXZ = 40°. Angle YXZ = 2 × 40° = 80° Step 2: Find the base angles of the isosceles triangle. Since XY = XZ, triangle XYZ is isosceles, so angle XYZ = angle XZY. Angle XZY = (180° − 80°) ÷ 2 = 100° ÷ 2 = 50° Step 3: Find angle XWZ using the angle sum in triangle XWZ. In △XWZ: angle WXZ + angle XZW + angle XWZ = 180° 40° + 50° + angle XWZ = 180° Angle XWZ = 180° − 90° = 90° Step 4: Find angle XWY. Angles XWY and XWZ are supplementary (they form a straight line at W on YZ). Angle XWY = 180° − 90° = 90° Step 5: Find the required sum. Angle XWY + angle XZY = 90° + 50° = 140°

Correct answer: 140°

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