The sum of two numbers a and b is 20. Write an expression for the sum of their squares, in terms of a.
a + b = 20 or b = 20-a
a^2 + (20-a)^2 = sum of squares in terms of 'a'
a^2 + a^2 -40a+400
2a^2 -40a+400 = sum of squares
+36915 
