Algebra and polygon angle measures (ACT). Game on.

Algebra and polygon angle measures (ACT) is a grade 9 math skill aligned to Common Core standard HSG.CO.C.9. Below are 8 practice questions with answers and step-by-step explanations, drawn from the 10 algebra and polygon angle measures (act) problems our math games drill.

CCSS HSG.CO.C.910 questions in the bank
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Warm-upeasy

In parallelogram PQRSPQRS, mP=(4x+6)°m\angle P=(4x+6)° and mQ=(2x+24)°m\angle Q=(2x+24)°. What is the measure of P\angle P?

Consecutive angles are supplementary: (4x+6)+(2x+24)=180(4x+6)+(2x+24)=180, so 6x+30=1806x+30=180 and x=25x=25. Then mP=4(25)+6=106°m\angle P=4(25)+6=106°.

Mid-gameeasy

Each interior angle of rectangle WXYZWXYZ measures (3x12)°(3x-12)°. What is the value of xx?

Every interior angle of a rectangle measures 90°90°, so 3x12=903x-12=90 and x=34x=34.

Mid-gameeasy

In ABC\triangle ABC, mA=(x+8)°m\angle A=(x+8)°, mB=(2x+17)°m\angle B=(2x+17)°, and mC=(x+55)°m\angle C=(x+55)°. What is the value of xx?

The three interior angles sum to 180°180°: (x+8)+(2x+17)+(x+55)=180(x+8)+(2x+17)+(x+55)=180, so 4x+80=1804x+80=180 and x=25x=25.

Mid-gameeasy

Two parallel lines are cut by a transversal. A pair of corresponding angles measure (3x+16)°(3x+16)° and (2x+34)°(2x+34)°. What is the measure of each of these angles?

Corresponding angles are congruent: 3x+16=2x+343x+16=2x+34, so x=18x=18. Each angle measures 3(18)+16=70°3(18)+16=70°.

Mid-gameeasy

Two parallel lines are cut by a transversal. Same-side interior angles measure (6x5)°(6x-5)° and (4x+15)°(4x+15)°. What is the value of xx?

Same-side interior angles are supplementary: (6x5)+(4x+15)=180(6x-5)+(4x+15)=180, so 10x+10=18010x+10=180 and x=17x=17.

Mid-gameeasy

Two parallel lines are cut by a transversal. A linear pair of adjacent angles measure (5x+10)°(5x+10)° and (3x+50)°(3x+50)°. What is the measure of the larger angle?

A linear pair is supplementary: (5x+10)+(3x+50)=180(5x+10)+(3x+50)=180, so 8x+60=1808x+60=180 and x=15x=15. The angles are 85°85° and 95°95°, so the larger is 95°95°.

Mid-gamemedium

In isosceles DEF\triangle DEF, the vertex angle measures (4x+10)°(4x+10)° and each base angle measures (65x)°(65-x)°. What is the measure of each base angle?

The three angles sum to 180°180°: 2(65x)+(4x+10)=1802(65-x)+(4x+10)=180, so 140+2x=180140+2x=180 and x=20x=20. Each base angle is 6520=45°65-20=45°.

Buzzer beatermedium

In GHI\triangle GHI, mG=(2x+5)°m\angle G=(2x+5)°, mH=(3x+5)°m\angle H=(3x+5)°, and mI=(x+50)°m\angle I=(x+50)°. What is the measure of the largest angle of the triangle?

The angles sum to 180°180°: (2x+5)+(3x+5)+(x+50)=180(2x+5)+(3x+5)+(x+50)=180, so 6x+60=1806x+60=180 and x=20x=20. The angles are 45°45°, 65°65°, and 70°70°, so the largest is 70°70°.

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