Q:

How to explain the process of deriving a mathematical expression-Number 2? 

suppose that we have derived two expression  as below. 
a = b+c  (1)
y = w-z  (2)
Now, suppose we've been asked to solve an integral.  to explain how to solve the integral, I say:

The integral can be solved from (1) and (2) under simple modifications.  To do so, we only need to ...

The integral can be solved using (1) and (2) under simple modifications.  To do so, we only need to ...

The integral can be solved by/via/through (1) and (2) under simple modifications.  To do so, we only need to ...

Questions:
1) Which one do you prefer?  
2) If there is a better option, I will be happy to know it. 

A:

I haven't seen the last choice used, but the first ones. 
The first two are commonly used. 
Another way I'd add is: by using (1) and (2), the integral can be solved ...

