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if sinx+sin2x=2

then find,cos2x+cos4x

vishwa sharma , 14 Years ago
Grade 10
anser 1 Answers
Jitender Singh

Last Activity: 10 Years ago

Ans:
sin^{2}x + sinx = 2
(sinx+2)(sinx-1) = 0
sinx = 1
is the only solution.
x = n\pi \pm \frac{\pi }{2}
cos2x + cos4x = cos2(n\pi \pm \frac{\pi }{2}) + cos4(n\pi \pm \frac{\pi }{2})
cos2x + cos4x = cos(2n\pi \pm \pi ) + cos(4n\pi \pm 2\pi ) = -1 + 1 = 0
Thanks & Regards
Jitender Singh
IIT Delhi
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