Answer:
B is only true and the correct option.
Explanation:
[tex]\left(cos90\right)\left(cos30\right)-\left(sin90\right)\left(sin30\right)[/tex]
- [tex]\quad \cos \left(90^{\circ \:}\right)=0[/tex]
- [tex]\quad \sin \left(90^{\circ \:}\right)=1[/tex]
- [tex]\quad \sin \left(30^{\circ \:}\right)=\frac{1}{2}[/tex]
- [tex]\cos \left(30^{\circ \:}\right)=\frac{\sqrt{3}}{2}[/tex]
when simplified:
[tex]\left(cos90\right)\left(cos30\right)-\left(sin90\right)\left(sin30\right) = \ -\frac{1}{2}[/tex]
from options:
A) [tex]cos60^\circ =\frac{1}{2}[/tex]
✔B) [tex]\cos \left(120^{\circ \:}\right) = -\frac{1}{2}[/tex]
C) [tex]sin60^\circ = \frac{\sqrt{3} }{2}[/tex]
D) [tex]sin120^\circ = \frac{\sqrt{3} }{2}[/tex]
