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8th grade Missing angles with letters: straight lines, corners and crossing lines worksheet

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Missing angles with letters: straight lines, corners and crossing lines

Grade 8 Math Worksheet - Building Confidence

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Circle the best answer, or write your answer on the line.

  1. Noah opens craft scissors, and the blades cross. Two angles across from each other are (3x + 12)° and (5x − 20)°. Which equation fits the sketch?

    • 3x + 12 + 5x − 20 = 90
    • 3x + 12 = 5x − 20
    • 3x + 12 + 5x − 20 = 180

  2. Pia's ramp board rests on flat ground. The angles on each side of it are (2x + 30)° and (4x)°. Which equation fits the sketch?

    • 2x + 30 + 4x = 90
    • 2x + 30 + 4x = 180
    • 2x + 30 = 4x

  3. Ren sews a straight seam out from the square corner of a quilt patch, splitting it into (x + 15)° and (2x)°. Which equation fits the sketch?

    • x + 15 + 2x = 90
    • x + 15 = 2x
    • x + 15 + 2x = 180

  4. Tala draws two straight paths crossing on paper. Two angles across from each other are (4x − 10)° and (2x + 30)°. Which equation fits the sketch?

    • 4x − 10 = 2x + 30
    • 4x − 10 + 2x + 30 = 180
    • 4x − 10 + 2x + 30 = 90

  5. Zee solved an angle equation and found x = 23. In the sketch, the door's angle is (3x + 11)°. How many degrees is it?

  6. Ari solved an angle equation and found x = 31. In the sketch, the kite string's angle is (4x + 6)°. How many degrees is it?

  7. Bo solved an angle equation and found x = 12. In the sketch, the angle between the clock hands is (6x + 15)°. How many degrees is it?

  8. Jun's ramp board rests on flat ground. The angles on its two sides are (2x + 16)° and (3x + 9)°. The sketch writes 180° along the ground. What is x?

  9. Luz's bike kickstand touches flat ground, making angles of (4x + 7)° and (x + 8)° on each side. The sketch writes 180°. What is x?

  10. Milo folds the square corner of a paper sheet, splitting it into (3x − 6)° and (x + 4)°. The sketch writes 90° in the corner. What is x?

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8th grade Missing angles with letters: straight lines, corners and crossing lines worksheet – printable
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About this worksheet

Missing angles with letters: straight lines, corners and crossing lines. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can tell from a sketch whether two angles are equal (across from each other), add to 180° (side by side on a line) or add to 90° (a square corner), and write the equation.
  • I can solve for x when both angles have x, and then find the angle the question asks for.
  • I can turn a word description into angle expressions and solve it.

Standard: state-only (CCSS 7.G.B.5)

Words to know

vertical angles: Angles across from each other where two lines cross: they are equal.

supplementary: Two angles that add to 180°, like side by side on a line.

complementary: Two angles that add to 90°, filling a square corner.

adjacent: Side by side, sharing a ray.

expression: A rule with x, like (3x + 12)°, standing for an angle.

Common mistakes

Your child mixed up angles across from each other with angles side by side. Angles across from each other at a crossing are equal; angles side by side on a straight line add to 180°.

Your child used 180° where the angles fill a square corner (90°), or 90° where they lie along a straight line (180°). Look for the square-corner mark or the straight line together.

Your child stopped before dividing. After taking the number away, the x term still has a number in front of it: divide by it to find one x.

Questions parents ask

What is the most common mistake with missing angles with letters: straight lines, corners and crossing lines?

Your child mixed up angles across from each other with angles side by side. Angles across from each other at a crossing are equal; angles side by side on a straight line add to 180°.

Are these 8th grade math worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

More grade 8 math

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