Supplementary angles
Initial explanation
When two angles together form a straight line, they form a 180º angle.
They are called supplementary angles.
x and y are supplementary (they together form a straight line).
This is
x + y = 180
Equation for n
Since x = (2n +12)º. Instead of x we are going to write 2n + 12.
And y = (3n + 18)º. Then we are going to write 3n + 18 instead of y.
This is
x + y = 180
↓
(2n + 12) + (3n + 18) = 180
2n + 12 + 3n + 18 = 180
Now we have an equation taht we can use to find n.
2n + 12 + 3n + 18 = 180
Solving the equation
We have the equation and we are going to simplify it:
2n + 12 + 3n + 18 = 180
↓ since 2n + 3n = 5n
5n + 12 +18 = 180
↓ since 12 + 18 = 30
5n + 30 = 180
Now, we can solve it:
5n + 30 = 180
↓ taking 30 to the right side (substracting 30 both sides)
5n + 30 - 30 = 180 - 30
↓ since 30 - 30 = 0
5n + 0 = 180 - 30
5n = 180 - 30 = 150
5n = 150
↓ taking 5 to the right side (dividing by 5 both sides)
5n = 150
5n/5 = 150/5
↓ since 5n/5 = n
n = 150/5 = 30
n = 30
Then, we have n = 30
Finding x
Since
x = 2ºn + 12º
then, replacing n = 30
x = 2º · 30 + 12º
x = 60º + 12º
x = 72º
Answer: C. 72º
