化简cos^2 a(2cos^2 a+3)-sin^2 a(2cos^2 a+3)-4sin^2 a cos^2 a +3

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化简cos^2 a(2cos^2 a+3)-sin^2 a(2cos^2 a+3)-4sin^2 a cos^2 a +3
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化简cos^2 a(2cos^2 a+3)-sin^2 a(2cos^2 a+3)-4sin^2 a cos^2 a +3
化简cos^2 a(2cos^2 a+3)-sin^2 a(2cos^2 a+3)-4sin^2 a cos^2 a +3

化简cos^2 a(2cos^2 a+3)-sin^2 a(2cos^2 a+3)-4sin^2 a cos^2 a +3
cos^2x(2cos^2x+3)-sin^2x(2cos^2x+3)-4sin^2xcos^2x+3=2cos^4x+3cos^2x-2cos^2xsin^2x-3sin^2x-4sin^2xcos^2x+3=2cos^4x+3cos^2x-6cos^2xsin^2x-3sin^2x+3=2cos^4x+3cos^2x-6cos^2x(1-cos^2x)-3(1-cos^2x)+3=2cos^4x+3cos^2x-6cos^2x+6cos^4x-3+3cos^2x+3=8cos^4x