Find y when x = 9 if y varies directly as the square of x, and y = 245 when x = 7.

Step-by-step explanation:

y is directly proportional to x^2.

This means that y = kx^2, where k is a real constant.

When x = 7, y = 245:

245 = k(7)^2 = 49k. By division, k = 5.

Now we know that y = 5x^2, when x = 9, y = 5(9)^2 = 5 * 81 = 405.