Q.

If α=limx→0+(etanx-extanx-x) and β=limx→0+(1+sinx)12cotx are the roots of the quadratic equation ax2+bx-e=0, then 24loge(a+b) is equal to _______


Ans.

(12)

α=limx→0+etanx-extanx-x=1, β=limx→0(1+sinx)12cotx=e1/2

The equation having roots 1, e is x2-(1+e)x+e=0

It is given as ax2+bx-e=0

By comparing we get a1=b-(1+e)=-11⇒a=-1, b=1+e

∴ 12loge(a+b)=12loge(-1+1+e)=6