回收。。。。。。
接着做：
原式=∫(0,π/2)a^4 sin²tcos²tdt
=a^4∫(0,π/2)(1-cos²t)cos²tdt
=a^4 [∫(0,π/2)cos²tdt-∫(0,π/2)cos^4tdt]
=a^4 ×【1/2 ×π/2-3/4×1/2 × π/2】
=a^4×π/16
=πa^4/16
原式=∫(0,π/2)a^4 sin²tcos²tdt
=a^4∫(0,π/2)(1-cos²t)cos²tdt
=a^4 [∫(0,π/2)cos²tdt-∫(0,π/2)cos^4tdt]
=a^4 ×【1/2 ×π/2-3/4×1/2 × π/2】
=a^4×π/16
=πa^4/16
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