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.

The first step to solve a quadratic equation that's set to zero is to factor the quadratic equation:

y² + 2y - 63 = 0
(y - 7)(y + 9) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (y - 7) or (y + 9) must equal zero:

If (y - 7) = 0, y must equal 7
If (y + 9) = 0, y must equal -9

So the solution is that y = 7 or -9

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

8a + 2x = -5a + 2x + 2
8a = -5a + 2x + 2 - 2x
8a + 5a = 2x + 2 - 2x
13a = + 2
a = \( \frac{ + 2}{13} \)
a = \( \frac{}{13} \) + \( \frac{2}{13} \)
a = x + \(\frac{2}{13}\)

Parallel lines are lines that share the same slope (steepness) and therefore never intersect. A transversal occurs when a set of parallel lines are crossed by another line. All of the angles formed by a transversal are called interior angles and angles in the same position on different parallel lines equal each other (a° = w°, b° = x°, c° = z°, d° = y°) and are called corresponding angles. Alternate interior angles are equal (a° = z°, b° = y°, c° = w°, d° = x°) and all acute angles (a° = c° = w° = z°) and all obtuse angles (b° = d° = x° = y°) equal each other. Same-side interior angles are supplementary and add up to 180° (e.g. a° + d° = 180°, d° + c° = 180°).

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

2a⁶ + 4a⁶ = 6a⁶