sin(arcsin(8x))
thats 8x
lol i did that wrong. its 1 or -1
actually 1/2 or -1/2, you know what i mean
you actually did it right looking at it, but you didnt actually take the square root
you won't be able to find an explicit formula for the inverse of a quintic. well, maybe you CAN, but it's pretty advanced stuff. i think. so just look for the value of x that will make f = 5.