More trig question

sin(arccos(3x))?

I did one like this in full yesterday.  I wish I could find it.  MMM

I'll talk you through it.

Let

theta = arccos(3x)         (becasuse remember acos returns an an angle)

Draw a right angled triangle and let one of the acute angles be theta

cos(theta) = 3x/1

so the adjacent side is 3x and the hypotenuse is 1

Use the  pythagorean theorum to find the opposite side.     sqrt(1^2-(3x)^2)

now read sin theta of the triangle :)

I'm the original poster so i found he answer to be sqrt(1-9x) using the pythagorean theorem.

I'm the original poster so i found he answer to be sqrt(1-9x) using the pythagorean theorem.

Almost - not quite, I think that you have made a careless error :)