清波荡漾
幼苗
共回答了17个问题采纳率:76.5% 举报
∫[0,+∞] e^(-x)dx ∫[0,+∞] e^(-2y)dy
=∫[0,+∞] e^(-x)dx { -1/2∫[0,+∞] e^(-2y)d(-2y) }
=∫[0,+∞] e^(-x)dx { -1/2 e^(-2y)|[0,+∞] }
=∫[0,+∞] e^(-x)dx { 1/2 }
= 1/2 [-∫[0,+∞] e^(-x)d(-x) ]
= 1/2 [-e^(-x)|[0,+∞] ]
= 1/2 [ 1 ]
= 1/2
1年前
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