If cos ⁡x=−4/5, and π

Question

If cos ⁡x=−4/5, and π<x<3π2, what is sin⁡(x+π/2)?

i really need help...

Anonymous · Accepted Answer

You sure do
perhaps you mean
If cos ⁡x=−4/5, and π<x<3π / 2, what is sin⁡(x+π/2)?
so x is in quadrant 3, this is a 3,4, 5 right triangle with x = -4, y = -3
keep going counterclockwise 90 degrees (π/2 radians) more
You are now in quadrant 4 with x = 3 and y = -4
the sin is then -4/5

frog · Answer

thank u!

oobleck · Answer

sin(x+π/2) = sinx cosπ/2 + cosx sinπ/2 = cosx

frog · Answer

hey obleck, how doi i use that in this: If tan⁡ x=√3, and 180°<x<270°, what is sin⁡(x−210°)?

frog · Answer

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