Question

Factor 8x3 − 343.

A) (2x − 7)(4x2 + 14x + 49)
B) (2x − 7)(4x2 + 28x + 49)
C) (2x − 7)(4x2 −14x + 49)
D) (2x − 7)(4x2 − 28x + 49)

Which expression is equivalent to 27x3 + 125?
A) (3x – 5)(9x2 – 15x + 25)
B) (3x – 5)(9x2 + 15x – 25)
C) (3x + 5)(9x2 – 15x + 25)
D) (3x + 5)(9x2 + 15x – 25)
please explain if you could, thank you

Answer 1

A) (2x − 7) (4x² + 14x + 49)

C) (3x + 5) (9x² − 15x + 25)

Explanation:

Sums and differences of cubes factor as:

a³ + b³ = (a + b) (a² − ab + b²)

a³ − b³ = (a − b) (a² + ab + b²)

8x³ − 343 is a difference of cubes.

(2x)³ − 7³

(2x − 7) (4x² + 14x + 49)

27x³ + 125 is a sum of cubes.

(3x)³ + 5³

(3x + 5) (9x² − 15x + 25)