math in hl HELP

[sweet777]

how exactly wud u solve d identity ques in trig?
plz give me an example and solve so dt i understand..............

[sweet777]

plzzzzzzzzzzzzzzz tell me fast

[astarmathsandphysics]

There are so many identity questins in trig. Do you have to prove an identity? Can you refer to a quaestion on a past paper?

[sweet777]

yea...basically proving an identity....for example:
(1-sinx)/(cosx) = (cosx)/(1+sinx)

[astarmathsandphysics]

yea...basically proving an identity....for example:
(1-sinx)/(cosx) = (cosx)/(1+sinx)

ok.Clear the fractions on both sides  byt multiplying by (cosx)(1+sinx)

This gives (1-sinx)(1+sinx)=(cosx)^2 then exand the left hand side to get

1-(sinx)^2=(cosx)^2 and add (sinx)^2 to both sides to get the basic identity 1=(sinx)^2+(cosx)^2

[sweet777]

thx....but umm..i guess i wrote it wrng...i meant dt using d 3 identities, prove that d Lhs=Rhs.....sry for writing it wrng

[astarmathsandphysics]

Is the question answered?

[IGSTUDENT]

Need some help in solving this equation:

k^3 = 2(k+8)^2

[Ghost Of Highbury]

k..simple algebra

---

first expand the right hand side and multiply it with 2

k³ = 2(k² + 16k 64)

k³ = 2k² + 32k + 128

now...get the right hand side to the left hand side

k³ - 2k² - 32k - 128 = 0


solve the cubic equation to get the answer

k=8 ;

[astarmathsandphysics]

I get the answers are complex numbers. Not nice ones either. Either the question is wrong or you have to use a numerical method. Can you check the question?

[Ghost Of Highbury]

i too think th q is rong...

8 fits though..

[IGSTUDENT]

Actually it is a GP question:

k/2, k+8, k^2 are in gp find k

[Ghost Of Highbury]

GP???

[astarmathsandphysics]

K=8 as adi said. When i say the question i thought there were 3 answers but there is only 1.

[Ghost Of Highbury]

wats GP