Question

Not sure what I'm doing wrong here...

Answer 1

I know that you have to use the formula cos A= - square root 1 - sin^2 A so cos A is -5/17

Answer 2

And for the double angle formula = 2 sin A cos A, plugging in the values I would multiply 2 (-8/17) (-15/17) = 240/289

Answer 3

If you have a question about anything let me know.
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You know the hypotenuse is always positive, and since you are in
the QIII, the adjacent side and the opposite side are both negative.

Knowing that the
1. opp=-8
2. hyp=17
you get, \((-8)\)\(^2+x^2=17^2 \quad \Longrightarrow \quad x=15\),
and since you are in QIII, adj=-15.

You are given that \(\sin(A)=-8/17\), and then you also know that
\(\cos(A)=-15/17\), based on the adjacent side we just found.

Answer 4

Nevermind, I see where I went wrong.. Small math error (:

Answer 5

Not also that \(\sin(2A)=2\sin(A)\cos(A)\),

and you already know \(\sin(A)\) and \(\cos(A)\).

Answer 6

I meant Note also (not, "not" also).

Answer 7

yes exactly @SolomonZelman