Question

Find an exact value.

cos 15°

Options:
A) sqrt 6 + sqrt 2 / 4
B) - sqrt2 + sqrt 6 / 4
C) - sqrt2 - sqrt 6 / 4
D) - sqrt6 + 1 / 4

Answer 1

A) \[ \frac{ \sqrt{6}+\sqrt{2} }{ 4 } \]
B) \[\frac{ -\sqrt{2} +\sqrt{6} }{ 4 }\]
C) \[\frac{ -\sqrt{2} - \sqrt{6} }{ 4 }\]
D) \[\frac{ -\sqrt{6} +1}{ 4 }\]

Answer 2

cos(a-b)=cosa cosb + sina sin b you know?
if ok
cos (45-30)= cos45 cos 30 +sin 45 sin 30

Answer 3

where did you get all the numebrs?

Answer 4

I dont get what you mean !

Answer 5

But its for cos 15° ?

Answer 6

It is an unknown angle
you have to make it bu known angle

Answer 7

you know that formula?
if yeah
put the numbers in it you will have answer (a)

Answer 8

I think I got it. Can you help with another?

Answer 9

Also, you can use \(\cos^2\frac x 2=\frac{1+\cos x}2\).

Answer 10

@klimenkov

Can you help with this one, pelase?
Write the expression as either the sine, cosine, or tangent of a single angle.

\[\cos(\frac{ \pi }{ 5 }) \cos(\frac{ \pi }{ 7 }) + \sin (\frac{ \pi }{ 5}) \sin (\frac{ \pi }{ 7 })\]

Answer 11

as "klimenkov " says you can use that formula shuch the way i draw