Question

Solve without using a calculator or tables:

(cos20 - cos100)/(sin100 - sin20)

Answer 1

I need to solve this like, if i have sin75 - sin15, it becomes sin(45 + 30) - sin(45 - 30), and then i use the sin(A + B) or whatever rule. so what i'm really asking is what values do i use, so that it becomes 2 special values?? (90,60,45,30) and its corresponding values in the circle (sin30 = sin150, etc)

Answer 2

well,,
you can easily see you have
2sin(60)sin(40)/ 2cos(60)sin(40)
=>tan 60 = sqrt(3)

Answer 3

how did you get there??

Answer 4

cos a - cos b = -2 sin(a+b/2)sin(a-b/2)
sin a -sin b = 2 cos(a+b/2) sin(a-b/2)

use these..

Answer 5

and how do you get that?? :P

Answer 6

you need to rote these things if you're preparing for an engineering exam, which i suppose you are..
anyways these have a very easy proof..if you wanna know we can discus..

Answer 7

oh....kay. thanks :)

Answer 8

glad to help..

Answer 9

why is this still open ?

Answer 10

because of reasons :P

Answer 11

what reasons ?