When t=0, u=x! ! ! ! ! !

When t=x, u=0! ! ! ! ! !

So the upper and lower integral limits of u are 0, x.

Note: it is not the upper and lower limit exchange of integral! ! ! You imagined it! !

After the variable is replaced, the integral limit will also change, but this question is only changed for you to understand as exchange.

Newman Hero 2065438+06051414: 00: 27

I hope it will be helpful to you and I hope it will be adopted.