Question

I need help with this question!!:D please.

Answer 1

@SolomonZelman Is this correct?

Answer 2

doesn't look correct

Answer 3

Ugh..How would I solve it?

Answer 4

you may use this :
\[\large \cos(x) = \cos(x+2\pi)\]

Answer 5

adding \(2\pi \) to the angle will not change the value of cos

Answer 6

\[\large \cos \left(-\dfrac{7 \pi}{4}\right)\]

Answer 7

\[\large = \cos \left(-\dfrac{7 \pi}{4} + 2\pi\right)\]

Answer 8

get a common denominator and add the fractions

Answer 9

\[\large = \cos \left(-\dfrac{7 \pi}{4} + \dfrac{8\pi}{4}\right)\]

Answer 10

\[\large = \cos \left(\dfrac{\pi}{4}\right)\]

Answer 11

whats the value of cos(pi/4) ?

Answer 12

0.7?

Answer 13

I got it. It's
\[\frac{ 1 }{ 2 }\]

Answer 14

we need to memorize values for few angles,
cos(pi/4) is one of them

Answer 15

\[\large \cos \left(\dfrac{\pi}{4}\right) = \dfrac{\sqrt{2}}{2}\]

Answer 16

Ok. I gotta question.

Answer 17

For example, if it says in my book:
sin (pi/4)=1/2 \[\sqrt{2}\]

Answer 18

Would it be \[\sqrt{2}\]
Or, it would stay just 1/2??

Answer 19

Cuz..That's how it is in my book.

Answer 20

\[\large \cos \left(\dfrac{\pi}{4}\right) = \dfrac{1}{\sqrt{2} }\]

Answer 21

like that ?

Answer 22

Yes. And then it just has a \[\sqrt{2}\] beside it.

Answer 23

cos (90+90+90+45)
cos 90 is = 0
therefore you're left with cos45

If you've memorised the special angles, you'll know that cos 45 is equal to