jika (x,y) = (2,3) merupakan penyelesaian dari ax + by = 1 dan ax - by = 7, nilai a + b adalah

ax + by = 1
ax - by = 7
--------------- +
2ax = 8
2a(2) = 8
4a = 8
a = 8/4
a = 2

ax + by = 1
2(2) + b(3) = 1
4 + 3b = 1
3b = 1 - 4
3b = - 3
b = - 3/3
b = - 1

a + b = 2 + (-1) = 2 - 1 = 1

Jadi nilai a + b adalah 1