Solve to find sin x , 4cos^2 + 7sin x -7 =0
4cos2 x + 7 sinx - 7 =0 we know that sin2 + cos2 = 1 so 4(1-sin2x) + 7sinx -7 = 0 if we times out the brackets -4sin2x + 7 sinx -3 =0 4sin2x -7sinx +3 =0 (4sinx-1)(sinx +2)=0 so therefore sinx =1/4 or -2 however we know sinx cannot be less than -1 so answer is only 1/4
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