Write the value of the expression

$\frac{1-4 \sin 10^{\circ} \sin 70^{\circ}}{2 \sin 10^{\circ}}$

$=\frac{1-2\left[2 \sin 10^{\circ} \sin 70^{\circ}\right]}{2 \sin 10^{\circ}}$

$=\frac{1-2\left[\cos \left(10^{\circ}-70^{\circ}\right)-\cos \left(10^{\circ}+70^{\circ}\right)\right]}{2 \sin 10^{\circ}}$

$=\frac{1-2\left[\cos \left(-60^{\circ}\right)-\cos 80^{\circ}\right]}{2 \sin 10^{\circ}}$

$=\frac{1-2\left[\cos 60^{\circ}-\cos 80^{\circ}\right]}{2 \sin 10^{\circ}}$

$=\frac{1-2\left[\frac{1}{2}-\cos \left(90^{\circ}-10^{\circ}\right)\right]}{2 \sin 10^{\circ}}$

$=\frac{1-2 \times \frac{1}{2}+2 \cos \left(90^{\circ}-10^{\circ}\right)}{2 \sin 10^{\circ}}$

$=\frac{2 \sin 10^{\circ}}{2 \sin 10^{\circ}}$

$=1$