x趋于0时 1-cosx 是sinx的,如何证明1 -cos x=sin x啊

(1-cosx^2)/x^

2sinx^2 =[1-1-2sin^2(x^2/2)]/x^

2sinx^2 =2sin^2(x^2/2)/x^

2sinx^2 =(x->0)2(x^2/2)^2/x^2*x^2=1/2