Question

How do you work out these??
a) cos(90°-x)
b) tan(180°+x)
c) sin(x+180°)

Answer 1

cos(A-B)=cosA cosB+sinA sinB

Answer 2

and cos90=0
sin90=1

Answer 3

tan (A + B) = (tan A + tan B)/(1 - (tan A)(tan B))
and tan180=0

Answer 4

sin (A + B) = (sin A)(cos B) + (cos A)(sin B)
and sin180=0
cos180=-1

Answer 5

I don't really understand what you're doing, but the question says simplify, if that helps.

Answer 6

yes
apply the rule

Answer 7

how?

Answer 8

@esamalaa how?

Answer 9

in a)
use the rule cos(A-B)=cosA cosB+sinA sinB
where in ur problem
A=90
B=x

Answer 10

i haven't learnt that rule, is there another way?

Answer 11

btw the answer for a) is sinx

Answer 12

Bahhh I'm trying to think of a good way to explain the first one >.<

Answer 13

The second one isn't too bad.

Answer 14

Tangent is periodic in pi ( or 180 degrees).
So if you add 180 degrees to the angle, it doesn't change tangent at all.
\[\Large\bf\sf \tan(180^o+x)\quad=\quad \tan(x)\]

Answer 15

Too weird? :U Confusing?
I could maybe draw a graph if it will help..

Answer 16

yes please i don't think i've learnt that before

Answer 17

Tangent is kind of a weird looking graph. Hopefully this doesn't make it more confusing lol.