Question

The cube root of $-729$ is:

• A. $-19$
• B. $-9$
• C. $-39$
• D. $-3$

Answer 1

Answer: (B)

$-9$

Prime factorising, we get,

$729=\left(9\right)\times \left(9\right)\times \left(9\right)$

But $-729=(-9)\times (-9)\times (-9)$

Then,

$\sqrt[3]{3-729}$ $=\sqrt[3]{3-9\times -9\times -9}=-9$

Therefore, cube root of $-729$ is $-9$

Hence, option $B$ is correct.