Prove a square can't be written $5x+ 3$, for all integers $x$. Homework question, should I use induction?.. 
Help please

Let $ A=\{y\in\mathbb{Z}: y=5x+3, x\in\mathbb{R} \}$
And, $y\in A \Rightarrow y$ are a multiple of 5 plus 3! The set of numbers that are multiples of 5 are $ \{...,-10,-5,0,5,10,...\} = \{n5: n \mathbb{Z} \}$
Think about it...
