if the sum of two positive numbers is 31and their product is 168,then the sum of their square is

Let the two numbers be a & b
We know,
(a+b)2=a2+b2+2ab
?or, a2+b2=(a+b)2-2ab
?Replacing values ab=168, a+b=31
a2+b2=312-2*168
a2+b2=961-336
a2+b2=625