Question

if a-b=10 and a^2-b^2=20, what is the value of b?

Answer 1

divide first equation into second gives a + b = 2
solving sumultaneously

a-b=10
a+b = 2
add
2a=12
a=6
so b =2-6 = -4

Answer 2

sorry i should of explained the division :

a^2-b^2 = (a-b)(a+b) (difference of 2 squares)

so a^2-b^2/(a-b) = (a-b)(a+b)/(a-b) = a+b

and of course 20/10 = 2