Missing Angles in Triangles Worksheet

**Page 1**

1.

Find the value of $x$ in the figure.

a. | 30 ^{o} | ||

b. | 45 ^{o} | ||

c. | 50 ^{o} | ||

d. | 60 ^{o} |

So, the triangle is an equilateral triangle.

In an equilateral triangle, the measure of each angle is equal to 60

So, the measure of

Correct answer : (4)

2.

Find the measure of $x$.

a. | 90° | ||

b. | 60° | ||

c. | 180° | ||

d. | 120° |

The sum of the measures of the three angles in the figure is 30° + 60° +

30° + 60° +

[Equate the sum of the measures of the three angles of the triangle to 180°.]

90° +

[Subtract 90 from each side.]

Correct answer : (1)

3.

Find the measure of the third angle.

a. | 90° | ||

b. | 120° | ||

c. | 100° | ||

d. | 110° |

In the triangle, the sum of all the 3 angle measures is 30° + 40° +

30° + 40° +

[Equate the sum of all the three angle measures of the triangle to 180°.]

70° +

[Subtract 70° from both sides.]

So, the measure of the third angle of the triangle is 110°.

Correct answer : (4)

4.

The measures of two angles of a triangle are 80° and 50°. Find the measure of the third angle.

a. | 70° | ||

b. | 50° | ||

c. | 60° | ||

d. | 40° |

Let

80° + 50° +

[Equate the sum of all the angle measures of the triangle to 180°.]

130° +

[Subtract 130° from both the sides.]

Correct answer : (2)

5.

What is the value of $x$ in the figure?

a. | 60° | ||

b. | 90° | ||

c. | 80° | ||

d. | 70° |

60° + 50° +

[Equate the sum of angles of the triangle to 180°.]

110° +

[Add.]

[Subtract 110° from each side.]

Correct answer : (4)

6.

Two angles in a triangle measure 30° and 14°. Find the measure of the third angle.

a. | 316° | ||

b. | 166° | ||

c. | cannot be determined. | ||

d. | 136° |

The measure of the third angle = 180 - (30 + 14)

[Given, two angles measure 30° and 14° .]

180 - (30 + 14) = 180 - 44 = 136

[Simplify.]

The measure of the third angle in the triangle is 136° .

Correct answer : (4)

7.

Find the sum of angle $x$° and angle $y$° in the right triangle.

a. | 90° | ||

b. | 270° | ||

c. | 120° | ||

d. | 180° |

The angles are

[Equate the sum of angles of the triangle to 180°.]

[Subtract 90° from each side.]

The sum of angle

Correct answer : (1)

8.

The triangle shown here is a right isosceles triangle. Find the values of $x$ and $y$.

a. | 60° and 60° | ||

b. | 45° and 45° | ||

c. | 60° and 45° | ||

d. | 45° and 60° |

The triangle is a right isosceles triangle. So

90° +

[Sum of the angles in a triangle.]

90° +

[Substitute

90° + 2

[Add

2

[Subtract 90° from each side.]

[Divide each side by 2.]

Correct answer : (2)

9.

Find the value of $x$ in the figure.

a. | 30° | ||

b. | 60° | ||

c. | 45° | ||

d. | 15° |

So, 90° + 60° +

[Simplify.]

So, the value of

Correct answer : (1)

10.

Two angles of a triangle measure 60° and 50°. Find the measure of the third angle.

a. | 65° | ||

b. | 80° | ||

c. | 70° | ||

d. | 75° |

The measure of the third angle = 180° - (60° + 50°).

= 70°

So the measure of the third angle is 70°.

Correct answer : (3)