# When y=125 and x=-3, what is the value of root3y-3x^4?

Jan 6, 2017

Let $x = - 3$
Let $y = 125$
$\sqrt[3]{y} - 3 {x}^{4} =$

$- 238$

#### Explanation:

$\sqrt[3]{y} - 3 {x}^{4}$

Let's break this down starting with $y$.

$\sqrt[3]{125} = 5$
because $n \cdot n \cdot n = {n}^{3}$ and $\sqrt[3]{{n}^{3}} = n$.

${5}^{3} = 125$ [how convenient :)]

$\sqrt[3]{125} = 5$

Now $x$.

$3 {\left(- 3\right)}^{4}$

Recall PEMDAS: Parentheses first, then exponents. You have to take account for that negative.

$- 3 \cdot - 3 \cdot - 3 \cdot - 3 = 81$

$81 \cdot 3 = 243$

Finally:

$5 - 243 = - 238$