Calculus

Since ∫ f(x) dx from x = a to x = b is F(b) - F(a) where F(x) is the integral of f(x).
So :
F(3) - F(0) = 4 ..............(1)
F(6) - F(3) = 4 ...............(2)
F(6) - F(2) = 5 .............(3)
(1) + (2) we get
F(6) - F(0) = 8 .............(4)
(4) - (3) we get
- F(0) + F(2) = 8 - 5 = 3
that is ∫ f(x) dx from x = 2 to x = 0 is 3.

2015-03-09 12:33:36 補充：
Correction : Last line should be from x = 0 to x = 2.