Question

cos(-247.5 DEGREES)

IN EXACT VALUE.
solve using half angle formula.

Answer 1

Hm.

Answer 2

add 360 degrees.

Answer 3

tell me what you get.

Answer 4

112.5

Answer 5

Now double that value!

Answer 6

ohh so cos 225 - sqroot 2 over 2?

Answer 7

You know the half angle formula?

Answer 8

I forgot it, but I can derive it on spot :D

Answer 9

yes cos u/2 = sqroot 1 + cos u/2

Answer 10

Yep.

Answer 11

http://mathworld.wolfram.com/Half-AngleFormulas.html

Answer 12

So, you should be fine. If you want to check your work, go to wolfram alpha, and just type in the cos(blah)

Answer 13

I have tried that on both wolfram and my calculator I get an exact amount

Answer 14

You get an exact amount, or you want one but they dont' give one?

Answer 15

i got the problem wrong... i got sqroot 2+sqroot2 all over 2

Answer 16

but it's wrong

Answer 17

Ok, lemme do some math

Answer 18

That's probaly a quadrant eror.

Answer 19

And, @lgbasallote

Answer 20

someone called?

Answer 21

Helpy out?

Answer 22

hmmm this seems difficult -__-- that or i just forgot my trig

Answer 23

Add 360 derees, then use 225 as the angle to find half of.

Answer 24

-247.5 bro.

Answer 25

\[
t =247.5 \\
2t= 495= 360 + 90 +45 \\
\cos(2t) =\ cos(90 + 45)=-\cos(45) = -\frac 1{\sqrt 2}\\
\cos^2(t)=\frac{ 1+ \cos(2t)}2=\frac {1-\frac 1{\sqrt 2}} {2}=\\
\frac{1}{2}-\frac{1}{2
\sqrt{2}}\\
\cos(t) = \pm \sqrt{\frac{1}{2}-\frac{1}{2
\sqrt{2}}}
\]

Answer 26

\[ \cos(t) = \cos(247.5)= -\sqrt{\frac{1}{2}-\frac{1}{2
\sqrt{2}}}= -0.382683
\]