# Sum and difference of angles - Examples, Exercises and Solutions

## Sum and Difference of Angles

We can add angles and get the result of their sum, and we can also subtract them to find the difference between them.
Even if the angles don't have any numbers, we'll learn how to represent their sum or difference and arrive at the correct result.

## Angle Sum

To find the sum of angles, they must have a common vertex.

## Difference Between Angles

Just as we have added angles, we can also subtract one from another.

We can say that:

$∡BAE+∡EAC=∡BAC$

## Practice Sum and difference of angles

### Exercise #1

Angle A equals 56°.
Angle B equals 89°.
Angle C equals 17°.

Can these angles make a triangle?

### Step-by-Step Solution

We add the three angles to see if they are equal to 180 degrees:

$56+89+17=162$

The sum of the given angles is not equal to 180, so they cannot form a triangle.

No.

### Exercise #2

Angle A equals 90°.
Angle B equals 115°.
Angle C equals 35°.

Can these angles form a triangle?

### Step-by-Step Solution

We add the three angles to see if they are equal to 180 degrees:

$90+115+35=240$
The sum of the given angles is not equal to 180, so they cannot form a triangle.

No.

### Exercise #3

Angle A is equal to 30°.
Angle B is equal to 60°.
Angle C is equal to 90°.

Can these angles form a triangle?

### Step-by-Step Solution

We add the three angles to see if they equal 180 degrees:

$30+60+90=180$
The sum of the angles equals 180, so they can form a triangle.

Yes

### Exercise #4

Triangle ADE is similar to isosceles triangle ABC.

Angle A is equal to 50°.

Calculate angle D.

### Step-by-Step Solution

Triangle ABC is isosceles, therefore angle B is equal to angle C. We can calculate them since the sum of the angles of a triangle is 180:

$180-50=130$

$130:2=65$

As the triangles are similar, DE is parallel to BC

Angles B and D are corresponding and, therefore, are equal.

B=D=65

$65$°

### Exercise #5

What kind of triangle is shown in the diagram below?

### Step-by-Step Solution

We calculate the sum of the angles of the triangle:

$117+53+21=191$

It seems that the sum of the angles of the triangle is not equal to 180°,

Therefore, the figure can not be a triangle and the drawing is incorrect.

The triangle is incorrect.

### Exercise #1

ABC is an isosceles triangle.

$∢A=4x$

$∢B=2x$

Calculate the value of x.

### Step-by-Step Solution

As we know that triangle ABC is isosceles.

$B=C=2X$

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

Therefore, we can calculate in the following way:

$2X+2X+4X=180$

$4X+4X=180$

$8X=180$

We divide the two sections by 8:

$\frac{8X}{8}=\frac{180}{8}$

$X=22.5$

22.5

### Exercise #2

Triangle ABC isosceles.

AB = BC

Calculate angle ABC and indicate its type.

### Step-by-Step Solution

Given that it is an isosceles triangle:$AB=BC$

It is possible to argue that:$BAC=ACB=45$

Since the sum of the angles of a triangle is 180, the angle ABC will be equal to:

$180-45-45=90$

Since the angle ABC measures 90 degrees, it is a right triangle.

90°, right angle.

### Exercise #3

$∢A=80$

$∢C=95$

$∢D=45$

Calculate the size of $∢B$.

### Step-by-Step Solution

We know that the sum of the angles of a quadrilateral is 360°, that is:

$A+B+C+D=360$

We replace the known data within the following formula:

$80+B+95+45=360$

$B+220=360$

We move the integers to one side, making sure to keep the appropriate sign:

$B=360-220$

$B=140$

140°

### Exercise #4

According to the data, calculate the size of $∢B$.

### Step-by-Step Solution

As we know, the sum of the angles in a square is equal to 360 degrees, therefore:

$360=A+B+C+D$

We replace the data we have in the previous formula:

$360=140+B+80+90$

$360=310+B$

Rearrange the sides and use the appropriate sign:

$360-310=B$

$50=B$

50

### Exercise #5

The angles below are between parallel lines.

What is the value of X?

### Step-by-Step Solution

In the first step, we will have to find the adjacent angle of the 94 angle.

Let's remember that adjacent angles are equal to 180, therefore:

$180-94=86$
Then let's observe the triangle.

Let's remember that the sum of the angles in a triangle is 180, therefore:

$180=x+53+86$

$180=x+139$

$180-139=x$

$x=41$

41°

### Exercise #1

AB||CD
AC||BD

Calculate angle $∢A$.

### Step-by-Step Solution

Angles ABC and DCB are alternate angles and equal to 45.

Angles ACB and DBC are alternate angles and equal to 45.

That is, angles B and C together equal 90 degrees.

Now we can calculate angle A, since we know that the sum of the angles of a square is 360:

$360-90-90-90=90$

90°

### Exercise #2

What is the value of X given the angles between parallel lines shown above?

### Step-by-Step Solution

Since the lines are parallel, we will draw another imaginary parallel line that crosses the angle of 110.

The angle adjacent to the angle 105 is equal to 75 (a straight angle is equal to 180 degrees) This angle is alternate with the angle that was divided using the imaginary line, therefore it is also equal to 75.

We are given that the whole angle is equal to 110 and we found only a part of it, we will indicate the second part of the angle as X since it changes and is equal to the existing angle X.

Now we can say that:

$75+x=100$

$x=110-75=35$

35°

### Exercise #3

In a right triangle, the sum of the two non-right angles is...?

90 degrees

### Exercise #4

What is the value of the void angle?

20

### Exercise #5

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