Suppose p>2 is a prime and $\displaystyle x^2+1$ is reducible in Fp[x]. Prove that the multiplicative group (Fp\{0},$\displaystyle \cdot$) contains an element of order 4. Deduce that p$\displaystyle \equiv$1mod4.

I'm finding algebra quite hard atm, and this question has got me stuck. I don't know where to start. Please help!