simple trig...but i just dont get it... (1 Viewer)

[mel871]

ive got this trig question with the solution and everything...i just dont understand how they got from one step to the next. it looks simple im just not getting it...

question:

prove cot (A + B) = (cotA cotB-1)/(cotA cotB)

solution:

(ok i understand all of RHS so ill just give u the LHS...)

LHS

cot(A + B)
=cos(A + B)/sin(A + B)
=(cosA cosB - sinA sinB)/(sinA cosB + cosA sinB) ....im not understanding how you get from the step b4, to this one...help plz =( it looks so simple...

 

[jake2.0]

its using the double angle formulas cos(A + B)=(cosA cosB - sinA sinB) and sin(A + B)=(sinA cosB + cosA sinB)

 

[mel871]

phew! extention stuff! i was stessing out for a minute there...thanx guys

 

[word.]

This is an extension 1 question and uses the compound angle formula taught in the extension 1 course.

 

[rnitya_25]

isn't double angles and stuff applicable in 2unit course also?
ive seen questions in 2unit papers....

 

[rama_v]

isn't double angles and stuff applicable in 2unit course also?
ive seen questions in 2unit papers....

nope
not in sylabus

 

[rnitya_25]

oh ok, my mistake. thanks for clarifying that.

 

[acmilan]

Last years 2 unit cssa had it, they got you to prove the sin(A + B) one, but they guided you through it.