I'm trying to figure out this mathbits homework. I don't think I'm getting this particular answer because the URL won't work.

Find the exact value of sinetheta when costheta = 3/5 and the terminal side of theta is in quadrant four

Thanks so much

2. Originally Posted by jlldbr216
I'm trying to figure out this mathbits homework. I don't think I'm getting this particular answer because the URL won't work.

Find the exact value of sinetheta when costheta = 3/5 and the terminal side of theta is in quadrant four

Thanks so much
All you need to do is draw a right triangle and solve it. Remember that $\displaystyle cos(\theta)=\frac{adjacent}{hypotenuse}$. The hypotenuse is 5, the adjacent side is 3, and so the pythagorean theorem gives $\displaystyle x^2=25-9=16$. So the remaining side is $\displaystyle x=4$. So sine should be $\displaystyle \pm\frac{4}{5}$. If the terminal side is in quadrant four, then what is the sign $\displaystyle \pm$ of sine?

$\displaystyle sin(\theta)=-\frac{4}{5}$