inverse trig question (1 Viewer)

[lolitaaa]

How do you do

sin(cos^-1 (-15/17)) ?

Thanks a lot!!

 

[Drongoski]

Draw a right-angled triangle, with sides: 8, 15, 17
cos^-1 (-15/17)) is in the 2nd quadrant. Looking at the triangle, the sine of this angle is + 8/17 (sine of the angle in the 2nd Quadrant is +ve)

So answer is: 8/17


ps: didn't you complete your HSC last year?

 

[braintic]

Alternatively:

Use the rule cos^-1 (-x) = pi - cos^-1 (x)

sin(cos^-1 (-15/17)) = sin (pi - cos^-1 (15/17)) = sin (cos^-1 (15/17)) [second quadrant angle]

THEN use your right-angled triangle to get 8/17