Step by step
The question
Question: if the exterior angle is 2x° and the far inside angles are 40° and 60°, 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 40 + 60 = 2x.
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.
Plain numbers go together.
40 + 60 = 100.
Now we have 100 = 2x.
Let's swap the two sides, so x is on the left.
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.
100 divided by 2 is 50.
So x = 50!
4 Check
Let's check: with x = 50, the inside angles are 40° and 60°.
Together 100°, 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.