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. 1.

   Bo's roof frame is an isosceles triangle with a top angle of 36°. The bottom beam sticks out past one bottom corner. How many degrees is the outside angle at that corner?

   108
2. 2.

   Esme's tent frame is an isosceles triangle with a top angle of 46°. The bottom beam sticks out past one bottom corner. How many degrees is the outside angle at that corner?

   113
3. 3.

   Jun's sail frame is an isosceles triangle with a top angle of 58°. The bottom beam sticks out past one bottom corner. How many degrees is the outside angle at that corner?

   119
4. 4.

   Luz extends two sides of triangle CDF. The outside angle at C is 128° and at D is 111°. How many degrees is the inside angle at F?

   59
5. 5.

   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
6. 6.

   Tala draws triangle CDF on paper and extends side CD past D. Why is the outside angle at D equal to angle C plus angle F?

   • The outside angle and the inside angle at D make 180°, and the three inside angles also make 180°
   • The outside angle and the inside angle at D make 360°, and the three inside angles make 180°
   • The outside angle is the biggest angle in the picture, so it is the sum of the others
7. 7.

   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°
   • Three copies fit corner to corner along a straight line, and a straight line is 180°
   • The triangle has a 90° corner, and the other two corners are 45° each, so 90 + 45 + 45 = 180
8. 8.

   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°
9. 9.

   Luz extends one side at each corner of triangle CDF, going around the same way. The outside angles are 128°, 111° and 121°. What do the three outside angles add to?

   • 540°: three straight lines
   • 180°: a straight line
   • 360°: a full turn
10. 10.

    Milo extends one side at each corner of triangle SUV, going around the same way. The outside angles are 140°, 119° and 101°. What do the three outside angles add to?

    • 180°: a straight line
    • 540°: three straight lines
    • 360°: a full turn