Examples with solutions for Sum and Difference of Angles: Finding the size of angles in a triangle

Exercise #1

Calculate the size of angle X given that the triangle is equilateral.

XXXAAABBBCCC

Video Solution

Step-by-Step Solution

Remember that the sum of angles in a triangle is equal to 180.

In an equilateral triangle, all sides and all angles are equal to each other.

Therefore, we will calculate as follows:

x+x+x=180 x+x+x=180

3x=180 3x=180

We divide both sides by 3:

x=60 x=60

Answer

60

Exercise #2

ABC is an equilateral triangle.8X8X8XAAABBBCCCCalculate X.

Video Solution

Step-by-Step Solution

Since this is an equilateral triangle, all angles are also equal.

As the sum of angles in a triangle is 180 degrees, each angle is equal to 60 degrees. (180:3=60)

From this, we can conclude that: 60=8x 60=8x

Let's divide both sides by 8:

608=8x8 \frac{60}{8}=\frac{8x}{8}

7.5=x 7.5=x

Answer

7.5

Exercise #3

Below is an equilateral triangle.

Calculate X.

X+5X+5X+5AAABBBCCC

Video Solution

Step-by-Step Solution

Since in an equilateral triangle all sides are equal and all angles are equal. It is also known that in a triangle the sum of angles is 180°, we can calculate X in the following way:

X+5+X+5+X+5=180 X+5+X+5+X+5=180

3X+15=180 3X+15=180

3X=18015 3X=180-15

3X=165 3X=165

Let's divide both sides by 3:

3X3=1653 \frac{3X}{3}=\frac{165}{3}

X=55 X=55

Answer

55

Exercise #4

Find all the angles of the isosceles triangle using the data in the figure.

626262AAABBBCCC

Video Solution

Step-by-Step Solution

In an isosceles triangle, the base angles are equal to each other—that is, angles C and B are equal.

C=B=62 C=B=62

Now we can calculate the vertex angle.

Remember that the sum of angles in a triangle is equal to 180 degrees, therefore:

A=1806262=56 A=180-62-62=56

The values of the angles in the triangle are 62, 62, and 56.

Answer

62, 62, 56

Exercise #5

Find all the angles of the isosceles triangle using the data in the figure.

707070AAABBBCCC

Video Solution

Step-by-Step Solution

Let's remember that in an isosceles triangle, the base angles are equal to each other.

In other words:

C=B C=B

Since we are given the vertex angle, which is equal to 70 degrees, we'll recall that the sum of angles in a triangle is equal to 180 degrees.

Now let's find the base angles in the following way:

18070=110 180-70=110

110:2=55 110:2=55

Therefore, the angle values in the triangle are: 55, 55, 70

Answer

70, 55, 55

Exercise #6

Find all the angles of the isosceles triangle using the data in the figure.

505050AAACCCBBB

Video Solution

Step-by-Step Solution

Since we are given that the triangle is isosceles, we will remember that the base angles are equal to each other.

That is:

B=C=50 B=C=50

Now we can calculate the vertex angle.

Since the sum of angles in a triangle is equal to 180 degrees, we will calculate the vertex angle as follows:

A=1805050=80 A=180-50-50=80

Therefore, the values of the angles in the triangle are: 80, 50, 50

Answer

A=80,C=50 A=80,C=50

Exercise #7

Find all the angles of the isosceles triangle using the data in the figure.

505050AAACCCBBB

Video Solution

Step-by-Step Solution

In an isosceles triangle, the base angles are equal to each other, meaning:

B=C B=C

Since we are given angle A, we can calculate the base angles as follows:

Let's remember that the sum of angles in a triangle is equal to 180 degrees.

18050=130 180-50=130

130:2=65 130:2=65

B=C=65 B=C=65

Answer

B=65,C=65 B=65,C=65

Exercise #8

Find the measure of the angle α \alpha

120120120AAABBBCCC27

Video Solution

Step-by-Step Solution

Let's remember that the sum of angles in a triangle is equal to 180 degrees.

Therefore, we will use the following formula:

A+B+C=180 A+B+C=180

Now let's input the known data:

120+27+α=180 120+27+\alpha=180

147+α=180 147+\alpha=180

We'll move the term to the other side and keep the appropriate sign:

α=180147 \alpha=180-147

α=33 \alpha=33

Answer

33

Exercise #9

Find the measure of the angle α \alpha

505050AAABBBCCC50

Video Solution

Step-by-Step Solution

Recall that the sum of angles in a triangle equals 180 degrees.

Therefore, we will use the following formula:

A+B+C=180 A+B+C=180

Now let's insert the known data:

α+50+50=180 \alpha+50+50=180

α+100=180 \alpha+100=180

We will simplify the expression and keep the appropriate sign:

α=180100 \alpha=180-100

α=80 \alpha=80

Answer

80

Exercise #10

Find the measure of the angle α \alpha

696969AAABBBCCC23

Video Solution

Step-by-Step Solution

Let's remember that the sum of angles in a triangle is equal to 180 degrees.

Therefore, we will use the following formula:

A+B+C=180 A+B+C=180

Now let's input the known data:

α+69+23=180 \alpha+69+23=180

α+92=180 \alpha+92=180

We'll move the term to the other side and keep the appropriate sign:

α=18092 \alpha=180-92

α=88 \alpha=88

Answer

88

Exercise #11

Find the measure of the angle α \alpha

808080AAABBBCCC55

Video Solution

Step-by-Step Solution

Let's remember that the sum of angles in a triangle is equal to 180 degrees.

Therefore, we will use the following formula:

A+B+C=180 A+B+C=180

Now let's input the known data:

80+55+α=180 80+55+\alpha=180

135+α=180 135+\alpha=180

We'll move the term to the other side and keep the appropriate sign:

α=180135 \alpha=180-135

α=45 \alpha=45

Answer

45

Exercise #12

Find the measure of the angle α \alpha

949494AAABBBCCC92

Video Solution

Step-by-Step Solution

It is known that the sum of angles in a triangle is 180 degrees.

Since we are given two angles, we can calculate a a

94+92=186 94+92=186

We should note that the sum of the two given angles is greater than 180 degrees.

Therefore, there is no solution possible.

Answer

There is no possibility of resolving

Exercise #13

Find the measure of the angle α \alpha

100100100AAABBBCCC90

Video Solution

Step-by-Step Solution

Let's remember that the sum of angles in a triangle is equal to 180.

Therefore, we will use the formula:

A+B+C=180 A+B+C=180

Let's input the known data:

100+α+90=180 100+\alpha+90=180

190+α=180 190+\alpha=180

α=180190 \alpha=180-190

We should note that it's not possible to get a negative result, and therefore there is no solution.

Answer

There is no possibility of resolving

Exercise #14

Find the size of angle α \alpha .

27.727.727.7AAABBBCCC41

Video Solution

Step-by-Step Solution

First let's remember that the sum of the angles in a triangle is equal to 180 degrees.

Therefore, we can use the formula:

A+B+C=180 A+B+C=180

Then we will substitute in the known data:

α+27.7+41=180 \alpha+27.7+41=180

α+68.7=180 \alpha+68.7=180

Finally, we will move the variable to the other side while maintaining the appropriate sign:

α=18068.7 \alpha=180-68.7

α=111.3 \alpha=111.3

Answer

111.3

Exercise #15

Identify which type of triangle appears in the drawing:

606060

Video Solution

Step-by-Step Solution

Let's remember that the sum of angles in a triangle equals 180 degrees.

Let's calculate alpha in the following way:

60+α+α2=180 60+\alpha+\frac{\alpha}{2}=180

60+112α=180 60+1\frac{1}{2}\alpha=180

112α=18060 1\frac{1}{2}\alpha=180-60

112α=120 1\frac{1}{2}\alpha=120

Let's divide both sides by 1.5:

α=80 \alpha=80

Now we can calculate the remaining angle in the triangle:

α2=802=40 \frac{\alpha}{2}=\frac{80}{2}=40

So in the triangle we have 3 angles: 60, 80, 40

All of them are less than 90 degrees, therefore all angles are acute angles and the triangle is an acute triangle.

Answer

Acute triangle

Exercise #16

Identify which type of triangle appears in the drawing:

XXX3X3X3X5X5X5X

Video Solution

Step-by-Step Solution

Let's remember that the sum of angles in a triangle equals 180 degrees.

Let's calculate X in the following way:

3x+5x+x=180 3x+5x+x=180

9x=180 9x=180

Let's divide both sides by 9:

x=20 x=20

Now let's calculate the angles:

3x=3×20=60 3x=3\times20=60

5x=5×20=100 5x=5\times20=100

This means that in the triangle we have 3 angles: 20, 60, 100

Since we have one angle that is greater than 90 degrees, meaning an obtuse angle, this is an obtuse triangle.

Answer

Obtuse triangle

Exercise #17

Look at the isosceles right triangle below. What are its angles?

Video Solution

Step-by-Step Solution

Let's remember that the sum of angles in a triangle is equal to 180 degrees.

In a right triangle, there is one right angle equal to 90 degrees.

In an isosceles triangle, the base angles are equal to each other.

Therefore, we can calculate this in the following way:

18090=90 180-90=90

90:2=45 90:2=45

In other words, the angle values in this triangle are: 90, 45, 45

Answer

90, 45, 45

Exercise #18

Three angles measure as follows: 60°, 50°, and 70°.

Is it possible that these are angles in a triangle?

Video Solution

Step-by-Step Solution

Recall that the sum of angles in a triangle equals 180 degrees.

Let's add the three angles to see if their sum equals 180:

60+50+70=180 60+50+70=180

Therefore, it is possible that these are the values of angles in some triangle.

Answer

Possible.

Exercise #19

Tree angles have the sizes 56°, 89°, and 17°.

Is it possible that these angles are in a triangle?

Video Solution

Step-by-Step Solution

Let's calculate the sum of the angles to see what total we get in this triangle:

56+89+17=162 56+89+17=162

The sum of angles in a triangle is 180 degrees, so this sum is not possible.

Answer

Impossible.

Exercise #20

Tree angles have the sizes 94°, 36.5°, and 49.5. Is it possible that these angles are in a triangle?

Video Solution

Step-by-Step Solution

Let's remember that the sum of angles in a triangle is equal to 180 degrees.

We'll add the three angles to see if their sum equals 180:

94+36.5+49.5=180 94+36.5+49.5=180

Therefore, these could be the values of angles in some triangle.

Answer

Possible.