Question

if cosx = 4/5 then sin2x = ?​

Answer 1

Answer:

x is in 3rd quadrant

cos x=-4/5

tan(x/2) = root {(1−cos x)/(1+cos x)}=root{ (1+4/5)/(1–4/5)}=root{ 9/5)/(1/5)}=root(9)=+3 and -3.

so,x=180+y then x/2=180/2+y/2=>90+y/2. tan is -ve in 2nd quadrant.

Answer 2

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Hope it helps you