x^3+x^10=[(x+1)-1]^3+[(x+1)-1]^10
a2(x+1)^2=C(3,2)(x+1)^2×(-1)^(3-2)+C(10,2)(x+1)^2×(-1)^(10-2)
a2=-C(3,2)+C(10,2)=-3+45=42