Question 167110: If y varies directly as the square of x, and y=7 when x=9, find y when x=7.
Answer by midwood_trail(310)   (Show Source):
You can put this solution on YOUR website! If y varies directly as the square of x, and y=7 when x=9, find y when x=7.
y varies directly as x^2 is written y = kx^2, where k is the constant of variation.
y = 7 when x = 9. Given this data, we first solve for k.
y = kx^2
7 = k(9)^2
7 = 81k
7/81 = k
We now multiply the value just found for k by 7^2 or 49 to find y.
y = (7/81)(7)^2
y = (7/81)(49)
y = 343/81
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