Step by step
The question
Question: find x when the angles 110° and x are supplementary.
1 Use the angle fact
Supplementary angles add up to 180°.
Together they make a straight line.
To remember: C comes before S in the alphabet.
90 comes before 180.
So we add the two angles and make it 180: 110 + x = 180.
Careful!
Supplementary means 180, not 90.
90 is for complementary angles.
2 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°.
3 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: remove the 110.
Last: check.