# U substitution problem

#### tmt

##### Active member
Hi, I'm working on a u substitution problem so that.

u = 3-x

so that

du = (-1) dx ,

or

(-1) du = dx .

With these equations you just switch content from one side to the other with no problems?

Thanks,

Tim

#### Ackbach

##### Indicium Physicus
Staff member
The manipulations you've done there are all fine. You just need to obey the rules of algebra. Algebra doesn't go away when you start studying calculus - indeed, calculus packs down your algebra!

#### tmt

##### Active member
The manipulations you've done there are all fine. You just need to obey the rules of algebra. Algebra doesn't go away when you start studying calculus - indeed, calculus packs down your algebra!
Yop, I see it now.