1-2cos^2(60)

Could also note that  cos(2θ) = 2cos²(θ)-1 so 1-2cos²(60) = -cos(120)

$${\mathtt{\,-\,}}\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}{\left({\mathtt{120}}^\circ\right)} = {\frac{{\mathtt{1}}}{{\mathtt{2}}}} = {\mathtt{0.5}}$$

The cosine of 60 = 1/2

So

1- 2 (1/2)^2 =

1 - 2 (1/4) = 1 - 2/4 =

1- 1/2 = 1/2