Worksheet

Angles of a triangle: the sum and the exterior angle

Grade 8 Math Worksheet - Challenge Me

NameDate

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

  1. Luz's sail is a triangle with angles x°, (2x)° and (3x + 30)°. How many degrees is the largest angle?

  2. Milo's roof is a triangle with angles x°, (3x)° and (2x + 30)°. How many degrees is the largest angle?

  3. Tala draws triangle HQS and extends side HQ past corner Q. Some of the angles use x. How many degrees is the outside angle at Q?

  4. Zee draws triangle UVW and extends side UV past corner V. Some of the angles use x. How many degrees is the outside angle at V?

  5. Ari draws triangle YCD and extends side YC past corner C. Some of the angles use x. How many degrees is the outside angle at C?

  6. Kira's kite frame is an isosceles triangle with a top angle of 76°. The bottom beam sticks out past one bottom corner. How many degrees is the outside angle at that corner?

  7. Milo extends two sides of triangle SUV. The outside angle at S is 137° and at U is 104°. How many degrees is the inside angle at V?

  8. Noah extends two sides of triangle HQS. The outside angle at H is 131° and at Q is 113°. How many degrees is the inside angle at S?

  9. Zee cuts three copies of a right triangle and lines them up along a ruler. Why do the three angles of the right triangle add to 180°?

    • Three copies fit corner to corner around a point, and a full turn is 360°
    • The triangle has a 90° corner, and the other two corners are 45° each, so 90 + 45 + 45 = 180
    • Three copies fit corner to corner along a straight line, and a straight line is 180°

  10. Ari draws triangle GHQ on paper and extends side GH past H. Why is the outside angle at H equal to angle G plus angle Q?

    • The outside angle is the biggest angle in the picture, so it is the sum of the others
    • The outside angle and the inside angle at H make 360°, and the three inside angles make 180°
    • The outside angle and the inside angle at H make 180°, and the three inside angles also make 180°
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Angles of a triangle: the sum and the exterior angle

Answer Key - Grade 8 Math Worksheet - Challenge Me

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

  1. Luz's sail is a triangle with angles x°, (2x)° and (3x + 30)°. How many degrees is the largest angle?

    105

  2. Milo's roof is a triangle with angles x°, (3x)° and (2x + 30)°. How many degrees is the largest angle?

    80

  3. Tala draws triangle HQS and extends side HQ past corner Q. Some of the angles use x. How many degrees is the outside angle at Q?

    110

  4. Zee draws triangle UVW and extends side UV past corner V. Some of the angles use x. How many degrees is the outside angle at V?

    125

  5. Ari draws triangle YCD and extends side YC past corner C. Some of the angles use x. How many degrees is the outside angle at C?

    75

  6. Kira's kite frame is an isosceles triangle with a top angle of 76°. The bottom beam sticks out past one bottom corner. How many degrees is the outside angle at that corner?

    128

  7. Milo extends two sides of triangle SUV. The outside angle at S is 137° and at U is 104°. How many degrees is the inside angle at V?

    61

  8. Noah extends two sides of triangle HQS. The outside angle at H is 131° and at Q is 113°. How many degrees is the inside angle at S?

    64

  9. Zee cuts three copies of a right triangle and lines them up along a ruler. Why do the three angles of the right triangle add to 180°?

    • Three copies fit corner to corner around a point, and a full turn is 360°
    • The triangle has a 90° corner, and the other two corners are 45° each, so 90 + 45 + 45 = 180
    • Three copies fit corner to corner along a straight line, and a straight line is 180°

  10. Ari draws triangle GHQ on paper and extends side GH past H. Why is the outside angle at H equal to angle G plus angle Q?

    • The outside angle is the biggest angle in the picture, so it is the sum of the others
    • The outside angle and the inside angle at H make 360°, and the three inside angles make 180°
    • The outside angle and the inside angle at H make 180°, and the three inside angles also make 180°