Step by step
The question
Question: if the exterior angle is 110° and the far inside angles are x° and x°, what is x?
The exterior angle is outside the triangle, on the pushed-out side.
1 Use the rule
The exterior angle is the two far inside angles added together.
So x + x = 110.
Careful!
The outside angle is not inside the triangle.
It does not go in the 180° sum.
2 Group like terms
Terms are the parts between the + and − signs.
Like terms are the same kind: same letters, same powers.
All the x terms go together.
x + x = 2x.
Now we have 2x = 110.
3 Remove the 2
2x means 2 times x.
We want just x.
To remove times 2, we divide by 2.
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.
2 divided by 2 is 1.
So just x is left.
110 divided by 2 is 55.
So x = 55!
4 Check
Let's check: with x = 55, the inside angles are 55° and 55°.
Together 110°, the outside angle.
So the answer is right!
Let's look back.
First: use the rule.
Then: group like terms.
Then: remove the 2.
Last: check.