用等价无穷小求参数个数的真题

=ln[(1-ax^2)/(1+ax^2)]

=ln{(1-ax^2)[1-ax^2+o(x3)]}

~ln[1-2ax^2+o(x3)]

~-2ax^2+o(x3)

右边/右手边

~ { sin[(6的平方根)* x]} 2

~6[x+o(x^2)]^2

~6x^2+o(x^3)

-2a=6，

a=-3