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Given that cos2x= 7 over 9 0<x<90, what is the value of sinx ?
 Mar 19, 2014
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Given that cos2x= 7 over 9 0<x<90, what is the value of sinx ?



cos(2x) =

1 - 2sin 2(x) = 7/9

2sin 2(x) = 2/9

sin 2(x) =1/9

sin(x) = +/- 1/3

x = arcsin(1/3) or x=arcsin(-1/3) BUT, arcsin(-1/3) is outside of [0,90] so we disregard it and thus

x = arcsin(1/3)
 Mar 19, 2014

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