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 multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(3a)(9ab) + (9a²)(8b)
(3 x 9)(a x a x b) + (9 x 8)(a² x b)
(27)(a¹⁺¹ x b) + (72)(a²b)
27a²b + 72a²b
99a²b

The volume of a cylinder is πr²h:

v = πr²h
v = π(1² x 1)
v = 1π

To factor a quadratic expression, apply the FOIL method (First, Outside, Inside, Last) in reverse. First, find the two Last terms that will multiply to produce -4 as well and sum (Inside, Outside) to equal -3. For this problem, those two numbers are -4 and 1. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - 3y - 4
y² + (-4 + 1)y + (-4 x 1)
(y - 4)(y + 1)

The entire length of this line is represented by AD which is AB + BD:

AD = AB + BD