由函数①C(x)=1+sum from n=1 to ∞(-1)~n(x^(2n))/((2n)!)(n∈N,x∈R), ②S(x)=sum from n=1 to ∞(-1)^(n-1)(x^(2n-1)/((2n-1)!)(n∈N,x∈R),的奇偶性,C(0)=1,S(O)=0,C^2(x)+S^2(x)=1,周期性,点[C(x),S(x)]与单位圆上点一一对应推出...由函数①C(x)=1+sum from n=1 to ∞(-1)~n(x^(2n))/((2n)!)(n∈N,x∈R), ②S(x)=sum from n=1 to ∞(-1)^(n-1)(x^(2n-1)/((2n-1)!)(n∈N,x∈R),的奇偶性,C(0)=1,S(O)=0,C^2(x)+S^2(x)=1,周期性,点[C(x),S(x)]与单位圆上点一一对应推出C(x)=cosx,S(x)=sinx。展开更多
文摘由函数①C(x)=1+sum from n=1 to ∞(-1)~n(x^(2n))/((2n)!)(n∈N,x∈R), ②S(x)=sum from n=1 to ∞(-1)^(n-1)(x^(2n-1)/((2n-1)!)(n∈N,x∈R),的奇偶性,C(0)=1,S(O)=0,C^2(x)+S^2(x)=1,周期性,点[C(x),S(x)]与单位圆上点一一对应推出C(x)=cosx,S(x)=sinx。