化简 sin(a-2π)sin(a+π)-2cos(a-π|2)sin(a-π)-cos^2(π|2+a)

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化简 sin(a-2π)sin(a+π)-2cos(a-π|2)sin(a-π)-cos^2(π|2+a)

化简 sin(a-2π)sin(a+π)-2cos(a-π|2)sin(a-π)-cos^2(π|2+a)
化简 sin(a-2π)sin(a+π)-2cos(a-π|2)sin(a-π)-cos^2(π|2+a)

化简 sin(a-2π)sin(a+π)-2cos(a-π|2)sin(a-π)-cos^2(π|2+a)
化简 sin(α-2π)sin(α+π)-2cos(α-π/2)sin(α-π)-cos²(π/2+α)
原式=-sin(2π-α)sin(π+α)+2cos(π/2-α)sin(π-α)-(-sinα)²
=-sin²α+2sin²α-sin²α=0