If sinx+20∘=2sin x cos 40∘, where x∈(0, π/2), then which of the following hold(s) good?
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a
cos 2x=1/2
b
cosec 4x=2
c
secx2=6−2
d
tanx2=(2−3)
answer is A.
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Detailed Solution
sin x cos 20∘+cos x sin 20∘=2sin x cos 40∘or sin 20∘ cos x=sin x 2cos 40∘−cos 20∘or tanx=sin20∘2cos40∘−cos20∘=sin20∘cos40∘+cos40∘−cos20∘=sin20∘cos40∘+2sin30∘sin−10∘=sin20∘sin50∘−sin10∘=sin20∘2cos30∘sin20∘=13 or x=30∘