Angles around a point 90, 120, x

Step by step

The question

Question: find x when the angles around a point are 90°, 120° and x.

1 Use the angle fact

Angles around a point add up to 360°.

That is one full turn.

So we add them all and make it 360: 90 + 120 + x = 360.

2 Group like terms

The plain numbers go together.

Now we have 210 + x = 360.

3 Remove the 210

We want x by itself.

The 210 is in the way.

To remove 210, we take away 210.

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.

210 and − 210 make zero.

Cross them out.

360 minus 210 is 150.

So x = 150.

The angle x is 150°.

4 Check

Let's check: put x = 150 back and add the angles.

They add up to 360°.

So x = 150 is right!

Let's look back.

First: use the angle fact.

Then: group like terms.

Then: remove the 210.

Last: check.