Angles around a line add up to 180°. Angles around a point add up to 360°. When two lines intersect, adjacent angles are supplementary (they add up to 180°) and angles across from either other are vertical (they're equal).

To solve this equation, repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the equal sign and the answer on the other.

7a + 9 = \( \frac{a}{9} \)
9 x (7a + 9) = a
(9 x 7a) + (9 x 9) = a
63a + 81 = a
63a + 81 - a = 0
63a - a = -81
62a = -81
a = \( \frac{-81}{62} \)
a = -1\(\frac{19}{62}\)

To solve this equation, isolate the variable for which you are solving (b) on one side of the equation and put everything else on the other side.

-8b - 3z = 6b - 7z - 4
-8b = 6b - 7z - 4 + 3z
-8b - 6b = -7z - 4 + 3z
-14b = -4z - 4
b = \( \frac{-4z - 4}{-14} \)
b = \( \frac{-4z}{-14} \) + \( \frac{-4}{-14} \)
b = \(\frac{2}{7}\)z + \(\frac{2}{7}\)

When solving an equation with two variables, replace the variables with the values given and then solve the now variable-free equation. (Remember order of operations, PEMDAS, Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.)

The circumference of a circle is the distance around its perimeter and equals π (approx. 3.14159) x diameter: c = π d. The area of a circle is π x (radius)² : a = π r².