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if cos x = 4/11 find cos 2A (HELP PLEASE)

Trigonometry
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by 2A do you mean 2x?
If that's the case, then your'e going to do arc cos of 4/11, which yields x, then plug that value of x into cos2x
i dnt get ti can you walk me through it

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Other answers:

ok so by 2A did you actually mean cos2x?
yes
why dont you simply use this gem of a formulla : cos 2x = (2cos^2 x) - 1 hope this helps..
no it doesnt help CAUSE I DNT KNOW HOW TO DO IT :(
nevermind,,i cant help you further then :/
Ok so use your graphing calculator and there should be a button that's like cos, and right above it you'll see cos^-1. Plug into your calcultar, cos^-1(4/11), because what that's saying is cos of the whatever that is, is going to be 4/11. Now you have x. Now plug whatever you got for x back into your calculator.
Back into the equation cos2x.
wait y am i doin cos-1 instead of cos
because that's how you're going to find x. It's just like how if you had x^2=4, you'd find the square root of both sides. In this case you're getting rid of the cos.
so 68,67631374
what do i do after
ok, so is that what you're getting for cos^-1(4/11)?
yea
ok you have that value for x, now plug that in for x in cos2x. So plug in cos(2*68.67). That SHOULD be how you do it, I haven't done stuff like this in two years.
so is it a -.7353878608
Yeah uhhhh that should be it, apologies if it isn't though, I don't have a calculator with me.
use to apply cos2x=cos^2x-sin^2x cox=4/11 sinx=squareroot( 1-cos^2x)

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