no of soln

Why it is said that no of roots of x3=0 is 3 repeated roots...

Then why sin(x)=1 has only one root in (0,pi)

12 Answers

62
Lokesh Verma ·

hmm.. interesting...

i get ur question.. it is very thought provoking... i will post somting may be in a bit.. cos i need to be convinced about my arguments first :)

62
Lokesh Verma ·

see my first "guess"

is that the concept of repeated roots is only for polynomials...

sin is not a polynomial in that sense... of course taylor's expansion does make everythign close to a polynomial...

33
Abhishek Priyam ·

Don't know sir said its related to degree of tangency or something like that......

x3 has degree of tangency 3 at x=0....
as up to second derivative it is zero at x=0;

this is true for sinx also at pi/2 cosx=0...
so should be two solns...

but he said its about convention so sinx =1 has one soln....

i think....

62
Lokesh Verma ·

hmm.. i guess ur sir has some point..

but i wud be interested in knowing the degree of tangency.. cos i never heard of something like this!

33
Abhishek Priyam ·

i got something at (in eng this time)

http://books.google.co.in/books?id=0ZwmLz_UTYoC&pg=PA60&dq="degree+of+tangency"#PPA60,M1

also
...
http://books.google.co.in/books?ct=result&q="degree+of+tangency"&btnG=Search+Books

33
Abhishek Priyam ·

Anyone on this
..

1
voldy ·

I didn't understand what the Q meant?

1
voldy ·

do u mean y sinx attains 1 at only one value in the given regoin ?

1
Honey Arora ·

i think no. of roots are defined by power of the polynomial.............as xn has n roots similarly x3 has 3 roots
bt if we take sin(x)=1
=> sin-1(1)=x ,so here also it depends upon power of x and second thing is interval in which it lies.............
i don't know hw right i m..........

341
Hari Shankar ·

The fundamental theorem of algebra is related to polynomials.

It says that the polynomial of degree n

aoz^n+a1z^{n-1}+...+an = 0

has at least one root in the field of complex numbers

From factor theorem we deduce that it has exactly n roots counting repeated roots.

sine is not regarded as a polynomial and hence the theorem doesnt apply

39
Dr.House ·

i was not fully satisfied with the discussion, so posted in mathlinks again...

u can see the explanation here

http://www.mathlinks.ro/viewtopic.php?t=304586

3
msp ·

well i have read something abt repeated roots.

if f(∂)=0 and f'(∂)=0 then ∂ is said to be a repeated root of f(x)

Your Answer

Close [X]