If α > β > 0 are the roots of the equation ax2 + bx + 1 = 0, and \(\lim\limits_{x \to \frac{1}{\alpha}}\left(\frac{1-cos(x^2+bx+a)}{2(1-ax)^2}\right)^{1/2}=\frac{1}{k}\left(\frac{1}{\beta}-\frac{1}{\alpha}\right),\) then k is equal to
(1) β
(2) 2α
(3) 2β
(4) α
