计算下列定积分:∫上限1下限0(xe^x)dx; ∫上限1e下限0xlnxdx;求过程!
计算下列定积分:∫上限1下限0(xe^x)dx; ∫上限1e下限0xlnxdx;求过程!
∫(0→1) xe^x dx = ∫(0→1) x d(e^x)
= xe^x - ∫(0→1) e^x dx
= [(1)e^(1) - (0)e^(0)] - e^x
= e - [e^(1) - e^(0)]
= e - e + 1
= 1
∫(0→e) xlnx dx = ∫(0→e) lnx d(x²/2)
= (1/2)x²lnx - (1/2)∫(0→e) x² d(lnx)
= [(1/2)(e²)ln(e) - (1/2)(0)] - (1/2)∫(0→e) x dx
= (1/2)e² - (1/2)(x²/2)
= (1/2)e² - (1/4)(e² - 0)
= (1/4)e²第一个算对了!第二个我书上的答案是e²/4+1/4=1/4(1+e²)可能你上限打错了吧,1e什麽意思?好意思!上限是个e,没有1!不好意思啊!∫ xlnx dx = ∫ lnx d(x²/2) = (1/2)∫ lnx d(x²) = (1/2)x²lnx - (1/2)∫ x² d(lnx) = (1/2)x²lnx - (1/2)∫ x²(1/x) dx = (1/2)x²lnx - (1/2)∫ x dx = (1/2)x²lnx - (1/2)(x²/2) + C = (1/2)x²lnx - (1/4)x² + C = (1/4)x²(2lnx - 1) + C 代入上下限得: = (1/4)(e²)[2ln(e) - 1] - (1/4)(0) = (1/4)(e²)(2 - 1) = e²/4 还有意见不?你要有鉴别能力,不只是光信答案就可以。谢谢了啊!一会给你发过去几道题!帮忙解答一下!