What is the value of [tex]$1-2 \sin ^2\left(105^{\circ}\right)$[/tex]?

A. [tex]-\frac{\sqrt{3}}{2}[/tex]
B. [tex]-\frac{1}{2}[/tex]
C. [tex]\frac{1}{2}[/tex]
D. [tex]\frac{\sqrt{3}}{2}[/tex]



Answer :

Let's evaluate the expression [tex]\(1 - 2 \sin^2 (105^\circ)\)[/tex] step by step.

1. Calculate [tex]\(\sin(105^\circ)\)[/tex]:
The value of [tex]\(\sin(105^\circ)\)[/tex] is approximately [tex]\(0.9659258262890683\)[/tex].

2. Square [tex]\(\sin(105^\circ)\)[/tex]:
[tex]\[ \sin^2(105^\circ) \approx (0.9659258262890683)^2 = 0.9330127018922194 \][/tex]

3. Multiply by 2:
[tex]\[ 2 \sin^2(105^\circ) \approx 2 \times 0.9330127018922194 = 1.8660254037844388 \][/tex]

4. Subtract from 1:
[tex]\[ 1 - 2 \sin^2(105^\circ) \approx 1 - 1.8660254037844388 = -0.8660254037844388 \][/tex]

Thus, the value of [tex]\(1 - 2 \sin^2 (105^\circ)\)[/tex] is [tex]\(-0.8660254037844388\)[/tex].

This matches the known value of [tex]\(-\frac{\sqrt{3}}{2}\)[/tex], hence the correct answer is:
[tex]\[ -\frac{\sqrt{3}}{2} \][/tex]