Question

Find y when x=9 if y varies directly as the square of x, and y=100 when x=5.

Answer 1

If y varies directly as the square of x, that means that y=k*x^2. Plugging y=100 and x=5 into it, we get 100=k*5^2=k*25. Dividing by both sides, we get k=100/25=4. Going back to the original equation, we now know that y=4*x^2. Plugging 9=x in, we get 4*9^2=4*81=324=y

Answer 2

Answer:

324

Step-by-step explanation:

Given : y varies directly as the square of x

To Find : Find y when x=9

Solution :

We are given that y varies directly as the square of x

$\Rightarrow y \propto x^2$

So, $\Rightarrow y= kx^2$ ---1

where k is the constant of proportionality

Now we are also given that y=100 when x=5.

Substitute the values in 1

$100= k(5)^2$

$100= 25k$

$\frac{100}{25}=k$

$4=k$

So, equation becomes  $y= 4x^2$

Now substitute  x= 9

$y= 4(9)^2$

$y=324$

Hence The value of y when x is 9 is 324