y=arctan(2x/(2-x^2))y'=(1+x^2/2)/[1+(x^2/2)^2]=(1+x^2/2)-(1+x^2/2)(x^2/2)^2+(1+x^2/2)(x^2/2)^4-(1+x^2/2)(x^2/2)^6+……=1+x^2/2-(x^2/2)^2-(x^2/2)^3+(x^2/2)^4+(x^2/2)^5-(x^2/2)^6-(x^2/2)^7+……=1+x^2/2-...