Question

Exact value of cos75 using identities

Answer 1

0,2588

Answer 2

cos(75)=cos(45+30) = cos 45 cos 30 - sin 45 sin 30

sin(30)=1/2
cos(30)= sqrt3 /2

sin(45)=cos(45)=1/sqrt2

Answer 3

just finish it of please.

Answer 4

plug in the values I gave you for cos and sin of 30 and 45, and simplify the problem as much as you can.

You can type/draw the steps you do and I'll help you.

Answer 5

I don't understand what you're asking me to do. Attached is an example problem of what I am supposed to do.

Answer 6

@SolomonZelman

Answer 7

so you needed to find cos(75) using a half-angle formula ?

Answer 8

Yes

Answer 9

can you remind me the half-angle formula for cos, I don;t remember it.

Answer 10

\[\cos \frac{ u }{ 2 } = \pm \sqrt \frac{ 1 + \cos u }{ 2 }\]

Answer 11

@SolomonZelman

Answer 12

connection snapped viewing through profile, anyway....

Answer 13

\[\huge\color{blue}{ Cos ( \frac{150}{2} )=±\sqrt{ \frac{1+\cos(150)}{2} } }\]

Answer 14

\[\frac{ \sqrt{6} - \sqrt{2} }{ 4 }\] I think this is the correct answer

Answer 15

ok, cos(150)= -sqrt3/2 (trig. table)

\[\huge\color{blue}{ Cos ( \frac{150}{2} )=±\sqrt{ \frac{1-\frac{ \sqrt{3}}{2} }{2} } }\]
\[\huge\color{blue}{ Cos ( \frac{150}{2} )=±\sqrt{ \frac{ \frac{2}{2}+\frac{ \sqrt{3}}{2} }{2} } }\]

sp far, hold...

Answer 16

- , not + in last blue, sorry.