Answer:
= [tex]Cos[/tex](162°)
Step-by-step explanation:
[tex]Cos^{2}[/tex](81°) - [tex]Sin^{2}[/tex](81°)
we know that;
[tex]Cos^{2}[/tex](x°) - [tex]Sin^{2}[/tex](x°) = [tex]Cos[/tex](2x°)
[tex]Cos^{2}[/tex](81°) - [tex]Sin^{2}[/tex](81°) = [tex]Cos[/tex](2 * 81°)
= [tex]Cos[/tex](162°)
