原式=1/sin²x+1/cos²x
=(cos²x+sin²x)/(sin²x*cos²x)
=1/(sin²x*cos²x)
=4/(2sinx*cosx)²
=4/sin²(2x)
故应当选择答案D.4/sin2^(2x)
化简：(1/sin^2(x))+ (1/cos^2(x))等于
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