sine curve in the form of y = a sin(pi/2x) that passes through the point (2.5,-9.546)

pi/2 * 5/2 = 5/4 pi

so, we want a sin(5/4 pi) = -9.546

Since sin 5/4 pi = -1/√2, we want

a (-1/√2) = -9.546
a = 13.5

So, y = 13.5 sin(pi/2 x)