Angles in a triangle 50, 60, x

Step by step

The question

Question: find x when the angles in a triangle are 50°, 60° and x.

1 Use the angle fact

The three angles in a triangle always add up to 180°.

So we add them all and make it 180: 50 + 60 + x = 180.

2 Group like terms

The plain numbers go together.

Now we have 110 + x = 180.

3 Remove the 110

We want x by itself.

The 110 is in the way.

To remove 110, we take away 110.

We do it on both sides.

Why both sides?

The = sign means both sides are the same amount.

If we change only one side, they are not the same any more.

110 and − 110 make zero.

Cross them out.

180 minus 110 is 70.

So x = 70.

The angle x is 70°.

4 Check

Let's check: put x = 70 back and add the angles.

They add up to 180°.

So x = 70 is right!

Let's look back.

First: use the angle fact.

Then: group like terms.

Then: remove the 110.

Last: check.