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Mathematics 7 Online
OpenStudy (anonymous):

d

OpenStudy (amistre64):

its just a quadratic in disguise

OpenStudy (anonymous):

\[14\sin X \cos X-14\sin X=-7,2\sin X \cos X=-1+2\sin X\] Squaring both sides, \[4\sin ^{2}x \cos ^{2}x=1+4\sin ^{2}x-4\sin x\] \[4\sin ^{2}x \left( 1-\sin ^{2}x \right)-1-4\sin ^{2}x+4\sin x=0\] \[-4\sin ^{4}x+4\sin x-1=0\]

OpenStudy (amistre64):

let u = sin(x) 7u^2 - 14u + 2 = -5

OpenStudy (anonymous):

is it sin2x orsin ^2 x

OpenStudy (amistre64):

:)

OpenStudy (anonymous):

so the answer is zero?

OpenStudy (amistre64):

what is the solution of: 7u^2 - 14u + 2 = -5

OpenStudy (jdoe0001):

\(\bf 7 sin^2(x) - 14 sin(x) + 2 = -5 \implies 7 sin^2(x) - 14 sin(x) + 7 = 0\\ 7[sin^2(x) - 2sin(x) + 1] = 0\\ \textit{let sin(x) = u as amistre64 said}\\ 7[x^2-2x+1] = 0\)

OpenStudy (amistre64):

7u^2 - 14u + 2 = -5 7u^2 - 14u + 7 = 0 u^2 - 2u + 1 = 0 (u-1)^2 = 0

OpenStudy (jdoe0001):

woops, made x instead of u, anyhow hhehe

OpenStudy (amistre64):

let sin(x) = chi :)

OpenStudy (jdoe0001):

chi chi chia

OpenStudy (jdoe0001):

kiimiilee then just solve the quadratic for "u" or sin(x)

OpenStudy (amistre64):

"all" solutions will require you to period the both angles by multiples of 2pi

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