Here is the problem- If cos(t) = -9/11 where pi<t<3pi/2, find the values of the following trigonometric functions. the answer has to be a fraction or an arithmetic expression, exact answers.

for:

cos(2t)

sin(2t)

cos(t/2)

sin(t/2)

Here is what I did. Given that cos(t)= -9/11

(opp)^2+(adj)^2=(hyp)^2

(opp)^2 + (-9)^2 + (11)^2

(opp)^2 =202

opp = -sqrt(202)

I also thought since cos(2t) = 2cos^2(x)-1 I could do this

-9/11 = 2cos^2(x)-1

2cos^2(x)=2/11

cos^2(x)=1/11

cos(x)=squrt(1/11) and the answer in the back of the book tells me I am wrong. If you could get me on track I would really appreciate it. I will reread the chapter and the section on this and maybe it will come to me.

Thank you for your time!!

Keith Stevens