Given that a + B is equal to two a + B + 1, find the value of ab

Given that a + B is equal to two a + B + 1, find the value of ab

a^2+b^2=2
a+b=1
(a+b)^2-2ab=a^2+b^2
1^2-2ab=2
2ab=2-1=1
ab=1/2