## kaylala 2 years ago Find the value of the following using the concepts of both addition and subtraction formulas and reference angle: sin 255

1. kaylala

@eliassaab

2. kaylala

@ganeshie8

3. kaylala

@Callisto

4. anonymous

$\sin (225)=-\sin (360-255)=-\sin (105)=-\sin (45+60)=\\-\sin (45)) \cos (60)-\sin (60) \cos (45)$

5. anonymous

$-\sin (45)) \cos (60)-\sin (60) \cos (45)=-\frac{1+\sqrt{3}}{2 \sqrt{2}}$

6. kaylala

why is it -sin(360-255) why the - sign there?

7. anonymous

$-\sin(360-255)=- \sin (-255) =-(-\sin( 255)) = \sin(255)$

8. anonymous

Did you understand it?

9. kaylala

no sorry where did you get that?

10. anonymous

If you add 360 to an angle you do not change the sine of that angle sin(360+y) = sin(y) sin( 360 +(-x)) =sin(-x) = -sin(x) If you do not know these elementary facts, please review them in your book or notes.

11. anonymous

Have you heard about periodic functions?

12. kaylala

have no heard of periodic functions ever @eliassaab