How to Find the Cubic Polynomial with Given three Zeroes ?
Here we are going to see, how to find cubic polynomial with given zeroes.
Question 1 :
Find a polynomial p of degree 3 such that −1, 2, and 3 are zeros of p and p(0) = 1.
Solution :
The zeroes of the polynomial are -1, 2 and 3.
x = -1, x = 2 and x = 3
From these values, we may find the factors.
The factors are (x + 1) (x - 2) (x - 3)
The required cubic polynomial will be
p(x) = k(x + 1) (x - 2) (x - 3)
p(x) = k(x + 1) (x2 - 5x + 6)
p(x) = k(x3 - 5x2 + 6x + x2 - 5x + 6)
p(x) = k(x3 - 4x2 + x + 6)
Given that p(0) = 1
p(0) = k(03 - 4(0)2 + 0 + 6)
1 = 6k
k = 1/6 = 1/6
p(x) = (1/6)(x3 - 4x2 + x + 6)
Hence the required polynomial is (1/6)(x3 - 4x2 + x + 6).
Question 2 :
Find a polynomial p of degree 3 such that −2, −1, and 4 are zeros of p and p(1) = 2.
Solution :
The zeroes of the polynomial are -2, -1 and 4
x = -2, x = -1 and x = 4
From these values, we may find the factors.
The factors are (x + 2) (x + 1) (x - 4)
The required cubic polynomial will be
p(x) = k(x + 2) (x + 1) (x - 4)
p(x) = k(x2 + 3x + 2) (x - 4)
p(x) = k(x3 - 4x2 + 3x2 - 12x + 2x - 8)
p(x) = k(x3 - x2 - 10x - 8)
Given that p(1) = 2
p(1) = k [(1)3 - 12 - 10(1) - 8]
2 = k (-18)
k = -1/9
p(x) = (-1/9)(x3 - x2 - 10x - 8)
After having gone through the stuff given above, we hope that the students would have understood "How to Find the Cubic Polynomial with Given three Zeroes".
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