SOLUTION: if f(x) varies directly with x^2, and f(x)=80 when x=4 find the value of f(7)

Algebra ->  Quadratic Equations and Parabolas -> SOLUTION: if f(x) varies directly with x^2, and f(x)=80 when x=4 find the value of f(7)      Log On


   

Question 1077501: if f(x) varies directly with x^2, and f(x)=80 when x=4 find the value of f(7)
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
I can say:
+f%28x%29+=+k%2Ax%5E2+
------------------
When +x=4+, +f%284%29+=+80+
+80+=+k%2A4%5E2+
+16k+=+80+
+k+=+5+
----------------
+f%28x%29+=+5x%5E2+
and
+f%287%29+=+5%2A7%5E2+
+f%287%29+=+5%2A49+
+f%287%29+=+245+