hey guys!!! could you please help me with this question that iv been stuck on for ages.....!!!!! ok here i go...

Let a and b be positive real numbers such that

(a^2) +(b^2)=1

Prove that (a^4)+(b^4) is greater than or equal to 1/2

plz help!!! i reeli dun understand the q

thanx guys!!!!! :)