If sinθ=3/5 and q terminates in the first quadrant, find the exact value of cos2q.

Question

jim_thompson5910 · Answer

Hint:

cos(2q) = ( cos(q) )^2 - ( sin(q) )^2

anonymous · Answer

What is q though?

jim_thompson5910 · Answer

oh i thought it said sin(q), my bad

jim_thompson5910 · Answer

I think q is the terminal point

anonymous · Answer

It's okai c:

anonymous · Answer

I have to figure out how much it equals so that I can get my answer :l

jim_thompson5910 · Answer

hmm major typo because they're referring to q as an angle when they say cos(2q)

jim_thompson5910 · Answer

does it give you a picture or diagram?

anonymous · Answer

It gives me nothing, just the possible answers

jim_thompson5910 · Answer

ok let me have a look at that and that might help

anonymous · Answer

And all the answers are fractions

jim_thompson5910 · Answer

ok

anonymous · Answer

okai one sec

jim_thompson5910 · Answer

alright

anonymous · Answer

3/5
9/25
3/10
7/25

jim_thompson5910 · Answer

ok if it's a typo and they mean cos(2theta), then


cos(2theta) = ( cos(theta) )^2 - ( sin(theta) )^2


cos(2theta) = ( 4/5 )^2 - ( 3/5 )^2


The reason how I know that cos(theta) = 4/5 is because if you draw a right triangle with legs x and 3 with hypotenuse 5, you'll find through the pythagorean theorem that x = 4

anonymous · Answer

Oh okai, yeah I was just stuck cuhs I had no idea how I would do that :l but yeah that makes more sense, I never thought it could be a typo

jim_thompson5910 · Answer

that's the only thing i can think of (esp if there's no pic) cause otherwise: where does q fit in?

anonymous · Answer

Haha I have no clue that's why I asked what is q? cx

jim_thompson5910 · Answer

yeah who knows lol