高数 求不定积分 答案如图2

2025-05-12 00:30:21
推荐回答(1个)
回答1:

作倒代换,令x=1/t
则dx=-1/t²·dt
x=√2时,t=√2/2
x→∞时,t→0

所以,
原式=∫[√2/2~0]t³/√(1+t²-t^4)·(-1/t²)dt

=-∫[√2/2~0]t/√(1+t²-t^4)·dt

=∫[0~√2/2]t/√(1+t²-t^4)·dt

=1/2·∫[0~1/2]1/√(1+u-u²)·du
【令u=t²,则du=2tdt
t=0时,u=0
t=√2/2时,u=1/2】

=1/2·∫[0~1/2]1/√[5/4-(u-1/2)²]·du

=1/2·arcsin[(u-1/2)/(√5/2)] |[0~1/2]
【基本积分公式:
∫1/√(a²-x²)·dx=arcsin(x/a)】

=0-1/2·arcsin(-1/√5)

=1/2·arcsin(1/√5)