1,f(x)=(x^2-1)(x^2+2)=x^4+x^2-2
f'(x)=4x^3+2x
2,y=cosx/x x=π y=-1/π
y'=(-xsinx+cosx)/x^2 x=π1/π^2
切线方程为：y+1/π=1/π^2(x-π) x-π^2y-2π=0