∫(x^3*√(1+x^2))dx=(1/2)∫(x²√(1+x²))dx²=(1/2)∫t√(1+t)dt=(1/2)[∫(t+1)√(t+1)d(t+1) - ∫√(t+1)d(t+1)]=(1/2)[∫(t+1)^(3/2)d(t+1) - ∫(t+1)^(1/2)d(t+1)]=(1/5)(t+1)^(5/2)-(1/3)(t+1)^(...