Question

If f(x) varies directly with x2, and f(x) = 75 when x = 5, find the value of f(4).



A.


100


B.


50


C.


48


D.


25

Answer 1

Remember that y is equal to f(x).
f(x) = k*x^2

75 = k*(5)^2

75 = k*25

75/25 = k

3 = k

k = 3

Answer 2

Now, the equation f(x) = k*x^2 is turned into

f(x) = 3x^2.

Answer 3

f(x)=k×x2

f(5)=75=k×52

75=25k
find k=3 and so
f(x)=3×x2
then
f(4)=3×42=3×16

Answer 4

Plug in x=4 to the equation f(x) = 3x^2, and you'll get the answer.

Answer 5

ok hold on one sec

Answer 6

answer is option C

Answer 7

So it's 48. :)

Answer 8

ok thanks

Answer 9

No problem!