SOLUTION: If f(x) varies directly with x, and f(x) = 45 when x = 9, find the value of f(x) when x = 3.

Algebra ->  Equations -> SOLUTION: If f(x) varies directly with x, and f(x) = 45 when x = 9, find the value of f(x) when x = 3.       Log On


   

Question 945454: If f(x) varies directly with x, and f(x) = 45 when x = 9, find the value of f(x) when x = 3.

Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

If f%28x%29 varies directly with x,there is a constant k which makes f%28x%29=kx
and if f%28x%29+=+45 when x+=+9, we can find a constant k:
45=k%2A9
45%2F9=k
5=k
so, equation is f%28x%29=5x
to find the value of f%28x%29 when x+=+3, plug x in f%28x%29=5x
f%283%29=5%2A3
f%283%29=15