f(x)
=kx ; 0≤x<3
=2-(1/2)x ; 3≤x≤4
=0 ; elsewhere
∫(-∞->+∞) f(x) dx = 1
∫(-∞->0) f(x) dx + ∫(0->3) f(x) dx+ ∫(3->4) f(x) dx+ ∫(4->+∞) f(x) dx = 1
0 + ∫(0->3) kx dx+ ∫(3->4) [2- (1/2)x] dx+ 0 = 1
∫(0->3) kx dx+ ∫(3->4) [2- (1/2)x] dx = 1
我哪里清楚的啊