Answer
y = 45 when x = 3
Step-by-step explanation:
[tex]\begin{gathered} \text{Given that y varies directly as the square of x} \\ \text{This implies that there is a positive relationship betwe}en\text{ y and the square of z} \\ \text{Mathematically, this can be expressed as} \\ y\text{ }\propto x^2 \\ To\text{ turn this expression into an equation, we n}eed\text{ to introduce a proportionality constant k} \\ y=kx^2 \\ \text{ According to the question, y = 20 and x = 2} \\ \text{From the above informaion we can find our k} \\ y=kx^2 \\ 20\text{ = k }\cdot2^2 \\ 20\text{ = k }\cdot\text{ 4} \\ \text{Divide both sides by 4} \\ \frac{20}{4}\text{ = }\frac{k\cdot\text{ 4}}{4} \\ k\text{ = 5} \\ \text{ Find y when }x\text{ = 3} \\ y=kx^2 \\ y\text{ = 5 }\cdot(3)^2 \\ y\text{ = 5 }\cdot\text{ 9} \\ y\text{ = 45} \end{gathered}[/tex]
