[tex] \int ^2_1 \frac{dx}{(3-5x)^2} [/tex]

[tex] u = 3-5x [/tex]

[tex] du = -5dx [/tex]

[tex] dx = -\frac{1}{5} du [/tex]

so, (with the 7 and 2 being negatives)

= [tex] -\frac{1}{5} \int^7_2 \frac{du}{u^2} [/tex]

= [tex] -\frac{1}{5} (-\frac{1}{u})]^7_2 [/tex]

But what I don't understand is how the [tex] u^2 [/tex] becomes just [tex] u [/tex].