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.
No comments:
Post a Comment