What is the value of 2cos²(105) − 1?

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

…

nothjing

step-by-step explanation:

the first option is the answer.