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

z² - 25 = 0
(z - 5)(z + 5) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (z - 5) or (z + 5) must equal zero:

If (z - 5) = 0, z must equal 5
If (z + 5) = 0, z must equal -5

So the solution is that z = 5 or -5

The surface area of a cylinder is 2πr² + 2πrh:

sa = 2πr² + 2πrh
sa = 2π(9²) + 2π(9 x 7)
sa = 2π(81) + 2π(63)
sa = (2 x 81)π + (2 x 63)π
sa = 162π + 126π
sa = 288π

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.

6a - 2a = 4a

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.)

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°).