Precalc

• 

  emyeuanht2001

  
  December 5th 2008, 12:01 am

• co' bai nay giai hoai ko duoc, can u guys help ???????
  
  CosB/(1 - tanB) + sinB/(1 - cotB) = sinB+cosB
  
  Another one:
  
  Sin(x + (3π/2) + sin((3π/2)- x) = -2cosx
  sorry π = radian (pie)
  
  ko biet ai con nho ko nua, ....thanks though...

• 

  mltr

  
  December 5th 2008, 12:18 am

• CosB/(1 - tanB) + sinB/(1 - cotB) = sinB+cosB .. prove left side equal right side
  
  use tanB = sinB/cosB & cotB = cosB/sinB
  left side
  ((cosB)^2 - (sinB)^2 )/(cosB - sinB) = (cosB-sinB)(cosB+sinB)/(cosB-sinB) = cosB + sinB
  
  second problem use formula
  sinA + sinB = 2sin((A+B)/2)*cos((A-B)/2) ... have fun

• 

  emyeuanht2001

  
  December 5th 2008, 1:06 am

• hey mltr !
  Van ko hieu cho nay
  ((cosB)^2 - (sinB)^2 )/(cosB - sinB)
  tai sao o problem nó đang plus, why you changed it to minus ?????
  i thought it still cosB^2 + sinB^2 / ..... chu ???

• 

  mltr

  
  December 5th 2008, 1:11 am

• because 1-cotB = (sinB-cosB)/sinB ... need to multiply by -1 to get cosB-sinB ==> you get -sin^2

• 

  emyeuanht2001

  
  December 5th 2008, 1:23 am

• wow, khâm phục wá, học tới toán mấy rùi mà giỏi thía.....
  Cám ơn nhiều nha, nhưng cái problem thứ 2, mình ko hiểu tại sao dùng fomula because
  sin((x Plus 3n/2)) + sin ((3n/2 minus)) mà, theyr not the same......i don't think we can use sinA plus sinB ????
  but thanks alot for helping me out.....

• 

  mltr

  
  December 5th 2008, 10:03 am

• emyeuanht2001 wrote:
  Cám ơn nhiều nha, nhưng cái problem thứ 2, mình ko hiểu tại sao dùng fomula because
  sin((x Plus 3n/2)) + sin ((3n/2 minus)) mà, theyr not the same......i don't think we can use sinA plus sinB ????
  but thanks alot for helping me out.....

  
  
  why not? Treat the whole thing inside () as A and/or B ... the formula is just general.
  or you can do the ... long way by expand sin(a+b) and sin(a-b) ... hehe

• 

  TaK

  
  December 5th 2008, 10:10 am

• long way nàh

• 

  mltr

  
  December 5th 2008, 10:11 am

• hehé .. why not, just the way to practice problem solving

• 

  TaK

  
  December 5th 2008, 10:14 am

• I am so dud with this crap .. I cant even remember tan= gì nũa

• 

  mltr

  
  December 5th 2008, 10:18 am

• TaK wrote:I am so dud with this crap .. I cant even remember tan= gì nũa

  
  
  haha .. I would like to forget them too, but after PE exams .. kaka .. too lazy to take it ... don't want to reviews (

• 

  vietbuidoi

  
  December 5th 2008, 12:58 pm

• nhớ dai ghê , mltr zữ wa , thui zọt lolz

• 

  emyeuanht2001

  
  December 5th 2008, 9:15 pm

• thanks mltr..............

• 

  LilrhymerZ

  
  December 5th 2008, 9:20 pm

• moving on to trig, next is sin cos tan just like urs ~_~