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

is it A?

Answer 2

" f(x) varies directly with x^2", so

f(x) = k*x^2

for some constant k

Answer 3

we know that "f(x) = 75 when x = 5", so...

f(x) = k*x^2

75 = k*(5)^2

75 = k*25

75/25 = k

3 = k

k = 3

Answer 4

ohhhhhh i get it

Answer 5

Which makes the equation turn from

f(x) = k*x^2

into

f(x) = 3x^2

Answer 6

now that you know the full function, you can plug in x = 4 and evaluate

Answer 7

so its 100....

Answer 8

no

Answer 9

plug x = 4 into f(x) = 3x^2 to get ???

Answer 10

144

Answer 11

no

Answer 12

you square before you multiply

Answer 13

exponents come before multiplication in PEMDAS

Answer 14

ohh of course

Answer 15

its 48

Answer 16

correct

Answer 17

thx

Answer 18

you're welcome