Question

Find the exact value of:

Answer 1

\(\Large\cos (-\frac{5\pi}{4})\)

Answer 2

the negative sign is throwing me off

Answer 3

\(\cos(-x)=\cos(x)\)

Answer 4

wait. so is it basically just saying \(\Large\cos (\frac{5\pi}{4})\)
o-o

Answer 5

correct

Answer 6

\[-\frac{ 1 }{ \sqrt{2} }\]

Answer 7

@matlee we all know how to use a calculator.

Answer 8

your smart , i hope you do

Answer 9

read the rules, if you can

Answer 10

cos(-5pi/4) = cos(5pi/4)
=cos(2pi -3pi/4)
=cos(3pi/4)
=cos(pi-pi/4)
=-cospi/4
=-1/sqrt(2)
Source: mathskey.com

Answer 11

@matlee and @bradely , please don't provide direct answers, I don't care what the source is.

So from what i see,
\(\Large\cos (-\frac{5\pi}{4}) = -\frac{\sqrt{2}}{2}\)

Answer 12

So what was the purpose of putting a negative sign in there? Just to throw of poor unsuspecting students? Or is there actually something I need to do about the said negative sign?

Answer 13

@Nnesha @zzr0ck3r

Answer 14

and @satellite73 thank you for the trig cheat sheet, lot of helpful things on there

Answer 15

cos is even function
cos(-x)= cos(x)
but careful sin and tan
sin(-x)=-sin(X) odd
tan(-x)=-tan(x)odd

Answer 16

about*

Answer 17

so if cos (-x)= cos(x)
then sec(-x)= ?

Answer 18

then sec(-x) would be sec(x), since sec is just the inverse function of cos

Answer 19

so -cos(-x)= ?

Answer 20

-cos(-x)= -cos(x)

Answer 21

yep!
there is an identity to prove cos(-x)=cos(x)
you'll learn n calc one i guess

Answer 22

funnnn

Answer 23

ye!

Answer 24

XD Thank you

Answer 25

np :=)

Answer 26

cos gives you the \(x\) value on the angle,



The bottom angle is the negative version of the top angle, but they both give the same x values.

Answer 27

I hope that makes sense.