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问题: 积分问题

求∫√(4-x^2) dx

解答:

∫√(4-x^2) dx
设x=2sint,dx=2costdt,t=arcsin(x/2),2cost=√(4-x^2)
∫√(4-x^2) dx=∫4cost * costdt=∫2(1+cos2t)dt
=2t+sin2t+C
=2arcsin(x/2)+2sint*(2cost/2)+C
=x/2 * √(4-x^2)+2arcsin(x/2)+C , x^2≤4