帮忙算一个定积分 我算来算去是4π/3 但是答案是π 请大家算算多少

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帮忙算一个定积分 我算来算去是4π/3  但是答案是π   请大家算算多少

帮忙算一个定积分 我算来算去是4π/3 但是答案是π 请大家算算多少
帮忙算一个定积分

我算来算去是4π/3  但是答案是π   请大家算算多少

帮忙算一个定积分 我算来算去是4π/3 但是答案是π 请大家算算多少
方法一:
(16/3)∫(0→π/2) cos⁴θ dθ
= (16/3) * 3!/4!* π/2
= (16/3)(3 * 1)/(4 * 2) * π/2
= π
方法二:
(16/3)∫(0→π/2) cos⁴θ dθ
= (16/3)∫(0→π/2) (cos²θ)² dθ
= (16/3)∫(0→π/2) [(1 + cos2θ)/2]² dθ
= (16/3)(1/4)∫(0→π/2) (1 + 2cos2θ + cos²2θ) dθ
= (4/3)∫(0→π/2) [1 + 2cos2θ + (1 + cos4θ)/2] dθ
= (4/3)∫(0→π/2) [3/2 + 2cos2θ + (1/2)cos4θ] dθ
= (4/3)[3θ/2 + sin2θ + (1/8)sin4θ] |(0→π/2)
= 4/3 * 3/2 * π/2
= π