How to find the value of sin[2cos^-1(-3/5)] without using calculator??

Question

anonymous · Answer

Let $$\cos^{-1}\frac{-3}{5} = A \implies \cos A = \frac{-3}{5} \implies \cos^2 A = \frac{9}{25}$$

$$\cos^2 A + \sin^2 A = 1 \implies \sin A = \sqrt{1-9/25} = \frac{4}{5} $$

We cant to find $$\sin 2A $$ which is equal to $$2\sin A \cos A $$.


Gogogogogogog

anonymous · Answer

Anwer is -24/25 and when i use with calculator it gives me that number...

anonymous · Answer

Cool; I did it without a calculator, using the method above, because I'm not a three year old baby.

anonymous · Answer

So what is your answer at then end of your method??
4/5??

anonymous · Answer

ah so just plug 4/5 to the equation
i got it thanks

anonymous · Answer

No.. The answer is 2 * sin A * cos A.

And I told you sin A = 4/5 and cos A = 3/5.

anonymous · Answer

cos A = -3/5 ***

anonymous · Answer

Thank you