If a-b = 4 and ab = 60, what is the value of a + b?

a + b = 16 or - 16.

Step-by-step explanation:

a - b = 4

ab = 60 so a = 60/b

Substituting for a in the first equation:

60/b - b = 4

60 - b^2 = 4b

b^2 + 4b - 60 = 0

(b + 10) b - 6) = 0

b = 6, - 10.

Therefore, from the first equation:

When b = - 10. a + 10 = 4 giving a = - 6 or

When b = 6, a - 6 = 4 giving a = 10.

So when a = - 6, b = - 10 and

when a = 10, b = 6.

So a + b is either 16 or - 16.