(A) ∫−11(∣x∣+1)dx
Since ∣x∣ is an even function, ∫−aaf(x)dx=2∫0af(x)dx
=2∫01(x+1)dx
=2[2x2+x]01
=2(21+1)
=2×23=3⟶(IV)
(B) ∫−22∣x+1∣dx
∣x+1∣=0 when x=−1, so splitting at x=−1:
For x<−1, ∣x+1∣=−(x+1)
For x≥−1, ∣x+1∣=(x+1)
=∫−2−1−(x+1)dx+∫−12(x+1)dx
First integral:
=[−2x2−x]−2−1
=(−21+1)−(−2+2)=21
Second integral:
=[2x2+x]−12
=(2+2)−(21−1)=4+21=29
=21+29=5⟶(III)
(C) ∫−113∣x2∣dx
Since x2≥0 always, ∣x2∣=x2. Also x2 is an even function.
=3×2∫01x2dx
=6[3x3]01
=6×31=2⟶(II)
(D) ∫−11x∣x∣dx
f(−x)=(−x)∣−x∣=−x∣x∣=−f(x)
Since f(x)=x∣x∣ is an odd function, ∫−aaf(x)dx=0
=0⟶(I)
(A) → (IV), (B) → (III), (C) → (II), (D) → (I)