(20 + 15 i)(15i - 20) =
(Type your answer in the form a + bi.)

answer

-625

foil

first foil (20 + 15i)(15i - 20) to get

(20 * 15i) + (20 * (-20)) + (15i * 15i) + (15i * (-20))

= (300i) + (-400) + (225) + (-300i)

combine like terms

combine the i terms together to get

(300i) + (-400) + (225) + (-300i)

300i - 400 + 225 - 300i

= -400 + 225

substitute -1 into i^2

remember that i = so = -1, and substitute this into -400 + 225i^2

-400 + 225i^2

= -400 + 225(-1)

= -400 -225

= -625

x= -3 and

step-by-step explanation:

to find the roots of a cubic, use division or factoring to find the factors then set equal to 0. as this is a difference of cubes, it factors into

where a is the cube root of .

here   this is 27 and the cube root of 27 is 3. so we write using the form:

.

set each factor to 0 and solve for x.

x-3=0

x=3

the quadratic expression does not factor and must be solved using the quadratic formula.

where a = 1, b=3, and c=9

this cubic has two complex roots.