Saturday, August 2, 2014

one factor of p(x) = 2x^3-9x^2-11x+30 please solve it

To solve: p(x) =
2x^3-9x^2-11x+30


Solution.


P(-2)
= 2(-2)^3-9(-2)^2-11(-2)+30


= -16-36
-11(-2)+30


= -52+52=0


So ,
x-(-2) = x+2 is a factor.


Therefore p(x )= p(x) =
2x^3-9x^2-11x+30= (x+2)(ax^2+bx+c). But a and c could easily guessed by equating  x^3
and constant terms: a= 2 and c = 15


Therefore,  p(x) =
2x^3-9x^2-11x+30 = (x+2)(2x^2+bx+15) = 0


Equating the
coefficients of x on both sides,


-11 = 15x+2k
Or


k = (-11-15)/2 = -13.


So
the required factors of p(x) are: (x+2) and
2x^2-13x+15.


But 2x^2-13x+15 = 2x^2
-10x-3x+15


=2x(x-5)-3(x-5)


=(x-5)(2x-3),
zeros are x=5 and x=3/2.


Therefore the zeros of p(x) are 
-2,  3/2 and 5, or are the solutions of p(x) = 0.

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