Question

What is the factored form of 5x − 625x4

Options:
A. 5x(1 + 5x)(1 - 5x + 25x2)
B. 5x(1 - 5x)(1 + 5x + 25x2)
C. (1 - 5x)(1 + 5x + 25x2)
D. (1 + 5x)(1 - 5x + 25x2)

Answer 1

B

Explanation:

5x - 625
`x^(4)` ← factor out 5x from each term

= 5x(1 - 125x³) ← this factor is a difference of cubes and factors in general as

a³ - b³ = (a - b)(a² + ab + b²) , then

1 - 125x³

= 1³ - (5x)³

= (1 - 5x) (1² + 5x(1) + (5x)² )

= (1 - 5x) (1 + 5x + 25x²)

Then

5x - 625
`x^(4)` = 5x(1 + 5x + 25x²)