Question

sin 645, what i am doing wrong

Answer 1

645 means sine is negative (lies in third quadrant)

sin(720-75) = -sin75

sin 75 = \[\frac{ \sqrt{3}-2 }{ 4\sqrt{2} }\]

Answer 2

@Kainui

Answer 3

I don't think that's sin(75) :)

Answer 4

I suggest subtracting 360 degrees, then reduce it by identities down to an angle between 0 and 90 degrees with the sign.

Answer 5

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

Answer 6

I mean... come on, sin(75) > 0
but...
\[\sqrt3 - 2 < 0\]

Answer 7

sin(45+30)

sin45cos30 - cos45sin30

Answer 8

Silly nameless...person...
\[\Large \sin(A+B) = \sin(A)\cos(B) \color{red}+\cos(A)\sin(B)\]

Answer 9

sin45cos30 + cos45sin30

Answer 10

Are you trying to evaluate sin(75) or are you trying to show that identity is true? I'm sort of confused now.

Answer 11

oh yes , @kainui nothing i made a terrible mistake , i added a - sign

Answer 12

maybe you're good to go now? ^^

Answer 13

and not that I'm completely doubting your arithmetic skill, but...
\[\large \sin(45) = \frac{\sqrt2}{2}=\cos(45)\]\[\large \sin(30) =\frac12 \]\[\large \cos(30) = \frac{\sqrt3}{2}\]

Answer 14

thanks ! hehe

Answer 15

My book has got sin 45 and cos as 1/root 2

Answer 16

It's wrong

Answer 17

It is the same. 1/sqrt(2) = sqrt(2) / 2

Answer 18

some books and teachers don't like radical in the denominator.

Answer 19

Silly :>

Answer 20

i have not slept from a long time

Answer 21

Then get some rest haha