Solve Diff. Eq. Problem Using Substitution Method - Step by Step Guide

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Problem:

y'=f(at+by+c) where a,b, and c are constants. Show that the substitution of x=at+by+c changes the equation to the separable equation x'=a+bf(x). Use this method to find the general solution of the equation y'=(y+t)^2


I really have no clue on this one. If someone could start me off in the right direction that would be great. I'm not seeing how they get that separable eq.
 
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Try writting the substitution as
x-at-c = by
Now take the derivative with respect to what I am assuming is the independent variable, t. The result should pop out at you.
 
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