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CEMC Gauss (Grade 8), 2026

Geometry Difficulty 1.2 Junior Find the answer Canada

Quadrilateral $RSTU$ is formed
by placing two equilateral triangles together, as shown.

The measure of $\angle RST$ is

Pick one

Solution

The measure of each of the three angles in an equilateral
triangle is $\dfrac{180\degree}{3}=60\degree$ .

Thus, $\angle RSU=\angle TSU=60\degree$ .

Since $\angle RST=\angle RSU+\angle TSU$ , then the measure of $\angle RST=60\degree+60\degree=120\degree$ .

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