Question

If a-b=4 and ab=21 fi d the value of a³-b³

Answer 1

Answer:

a^3-b^3=(a-b)^3+3ab(a-b)

=4^3 +3*21(4)

=64+252

=316

Answer 2

$\Huge{\purple{\underline{\textsf{Answer}}}}$

$\large{\red{\underline{\tt{Given:}}}}$

a - b = 4

ab = 21

$\large{\red{\underline{\tt{To find:}}}}$

The value of a³-b³.

Step-by-step explanation:

$\large{\red{\underline{\tt{Solution:}}}}$

$\implies\rm (a-b)^3</p><p>$

$\implies\rm a^3-3a^2b+3ab^2-b^3$

$\implies\rm a^3-3ab(a-b)-b^3$

$\implies\rm 4^3=a^3-b^3-3(21)(4)$

$\implies\rm 64+252=a^3-b^3$

$\implies\rm a^3-b^3=<strong>316</strong>$