if the difference of two positive integer is 4,and the difference of their square is 80,what is the sum of ?
a-b = 4
a^2-b^2 = 80
(a-b)(a+b) = 80
4 (a+b) = 80
a+b = 20
a-b = 4
------------ add
2 a = 24
a = 12
so b = 8
a^2-b^2 = 80
(a-b)(a+b) = 80
4 (a+b) = 80
a+b = 20
a-b = 4
------------ add
2 a = 24
a = 12
so b = 8