2x integration integral 2x dx integrate 2x dx from 10 to 13 integrate 2x/1+x^2 integral 2x/1+x^2 dx integrate 2x^2 integral 2x+4/x^2+3x+1 integrate 2x/(x^2+1)(x^2+3) integrate 2x+3/5x^2+1 integral 2x sin(x^2+1)