here he didn't put the minus in the second step ! why ?
Notice that the limits are "reversed" in the second step.......
Remember that......
b a
∫ f(x) dx = - ∫ f(x) dx
a b
Yep that is why !
oooohhhhhhh right .... hhhhhhh I felt for a moment that I'm squint
thank you CPhill
