Polynomial Equation and its Roots

We will discuss here about the polynomial equation and its roots.

If f(x) is a polynomial in x of degree ≥  1 whose coefficients are real or complex numbers then f(x) = 0 is called its corresponding polynomial equation.


Examples of polynomial equation:

(i) 5x\(^{2}\) + 2 x - 7 is a quadratic polynomial and 5x\(^{2}\) + 2 x - 7 = 0 is its corresponding quadratic equation.


(ii) 2x\(^{3}\) + x\(^{2}\) + 5x - 3 is a cubic polynomial and 2x\(^{3}\) + x\(^{2}\) + 5x - 3 = 0 is its corresponding cubic equation.


(iii) x\(^{4}\) + x\(^{2}\) - 2x + 6  is a cubic polynomial and x\(^{4}\) + x\(^{2}\) - 2x + 6 = 0 is its corresponding cubic equation.



(iv) x\(^{5}\) + 2x\(^{4}\) + 2x\(^{3}\) + 4x\(^{2}\) + x + 2 is a cubic polynomial and x\(^{5}\) + 2x\(^{4}\) + 2x\(^{3}\) + 4x\(^{2}\) + x + = 0 is its corresponding equation.


If α be a value of x for which f(x) becomes zero, i.e., f(α) = 0, then α is said to be a root of the equation f(x) n= 0.

In other words,

α is called a root of the polynomial equation f(x) = 0 if f(α) = 0.


Examples of root of the polynomial equation:

(i) Let f(x) = 4x\(^{3}\) + 12x\(^{2}\) - 4x - 12. As 4(1)\(^{3}\) + 12(1)\(^{2}\) - 4(1) - 12 = 4 + 12 - 4 - 12= 0, i.e., f(1) = 0, f(x) = 0 has a root x = 1.


(ii) Let f(x) = x\(^{2}\) - 2x - 3. As (-1)\(^{2}\) - 2(-1) - 3 = 1 + 2 - 3 = 0, i.e., f(-1) = 0, f(x) = 0 has a root x = -1


(iii) Let f(x) = x\(^{4}\) + x\(^{3}\) – 2x\(^{2}\) + 4x - 24. As (2)\(^{4}\) + (2)\(^{3}\) - 2(2)\(^{2}\) + 4(2)  - 24 = 16 + 8 – 8 +8 + 8 = 0, i.e., f(2) =0, f(x) has a root x = 2


(iv) Let f(x) = x\(^{3}\) + x\(^{2}\) - x - 1. As (1)\(^{3}\) + (1)\(^{2}\) – (1) – 1 = 1 + 1 - 1 - 1 = 0, i.e., f(1) = 0, f(x) = 0 has a root x = 1.















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