Answer:
0.86602540
Step-by-step explanation:
Apply the cosine double-angle identity.
cos
(
2
⋅
105
)
Multiply
2
by
105
.
cos
(
210
)
Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because cosine is negative in the third quadrant.
−
cos
(
30
)
The exact value of
cos
(
30
)
is
√
3
2
.
−
√
3
2
The result can be shown in multiple forms.
Exact Form:
−
√
3
2
Decimal Form:
−
0.86602540
…
