arcsinx=x+ 1/6x^3+o(x^3)

tanx=x+ 1/3x^3+o(x^3)

arctanx=x- 1/3x^3+o(x^3)

cosx= 1- 1/2x^2+ 1/24x^4

ln( 1+x)=x- 1/2x^2+ 1/3x^3+o(x^3)

e^x= 1+x+ 1/2x^2+ 1/3x^3+...+o(x^3)

( 1+x)^2= 1+2x+a(a- 1)^2x^2/2！