f(x)=xsin²x=x(1-cos2x)/2=(1/2)x[1-(1-(2x)²/2!+(2x)^4/4!-...)]=(1/2)x[2²x²/2!-2^4x^4/4!+2^6x^6/6!-.....]=x³-2^3x^5/4!+2^5x^7/6!-........ -(-1)^n * 2^(2n-1)*x^(2n+1)/(2n!)-...
