SOLUTION: Please help me solve this problem : Let M and N be the root of an equation x^2+ax+b=0 and let O and P be the roots of x^2+cx+d=0. Express (M-O)(N-O)(M-P)(N-P) in terms of the

Algebra ->  Coordinate Systems and Linear Equations -> SOLUTION: Please help me solve this problem : Let M and N be the root of an equation x^2+ax+b=0 and let O and P be the roots of x^2+cx+d=0. Express (M-O)(N-O)(M-P)(N-P) in terms of the      Log On


   



Question 1075157: Please help me solve this problem :
Let M and N be the root of an equation x^2+ax+b=0 and
let O and P be the roots of x^2+cx+d=0. Express
(M-O)(N-O)(M-P)(N-P) in terms of the coefficients
a,b,c,d.

Found 2 solutions by Edwin McCravy, ikleyn:
Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
Let M and N be the root of an equation x^2+ax+b=0 and
let O and P be the roots of x^2+cx+d=0. Express
(M-O)(N-O)(M-P)(N-P) in terms of the coefficients
a,b,c,d.
M+=+%28-a%2Bsqrt%28a%5E2-4b%29%29%2F2

N+=+%28-a-sqrt%28a%5E2-4b%29%29%2F2

O+=+%28-c%2Bsqrt%28c%5E2-4d%29%29%2F2

P+=+%28-c-sqrt%28c%5E2-4d%29%29%2F2

Therefore:

%28M-O%29%28N-O%29%28M-P%29%28N-P%29%22%22=%22%22



I agree it isn't simplified, but it does express 
(M-O)(N-O)(M-P)(N-P) in terms of the coefficients a,b,c,d.
Nothing was mentioned about "in simplest form".

Edwin


Answer by ikleyn(52793) About Me  (Show Source):
You can put this solution on YOUR website!
.
1.  (M-O)*(N-O) = MN+-+ON+-OM+%2BO%5E2 

                = b+-+O%2A%28M%2BN%29+%2B+O%5E2          (I replaced MN by b based on Vieta's formulas)

                = b+%2B+cO+%2BO%5E2     (1)      (I replaced M+N by -c  based on Vieta's formulas)



2.  (M-P)*(N-P) = MN+-+PN+-PM+%2BP%5E2 

                = b+-+P%2A%28M%2BN%29+%2B+P%5E2          (I replaced MN by b based on Vieta's formulas)

                = b+%2B+cP+%2B+P%5E2     (2)      (I replaced M+N by -c  based on Vieta's formulas)



3.  (M-O)*(N-O)*(M-P)*(N-P) = %28b+%2B+cO+%2BO%5E2%29%2A%28b+%2B+cP+%2BP%5E2%29 =  (I used here (1) and (2) )

    =  = 

    =  = 

    =  = 

    = b%5E2+-+bc%5E2+%2B+b%2A%28%28-c%29%5E2-2d%29+%2B+c%5E2d+-+c%5E2d+%2B+d%5E2


         ( I replaced here P+O by -c, P%5E2+%2B+O%5E2 by %28P%2BO%29%5E2-2PO%29, and PO by d. )

    = b%5E2+-+bc%5E2+%2B+b%2A%28c%5E2-2d%29+%2B+d%5E2 = b%5E2+-+2bd+%2B+d%5E2 = %28b-d%29%5E2.     ( !!! )

Done.


Check my Math. I could make a mistake.

But the major idea is VERY CLEAR:

     make multiplications and use everywhere the Vieta's formulas for quadratic polynomials: 


         the sum of the roots is the coef. at x with the opposite sign; the product of the roots is the constant term.