Relation between root and coefficient
Answers
The sum of the roots of a quadratic equation is equal to the negation of the coefficient of the second term, divided by the leading coefficient. The product of the roots of a quadratic equation is equal to the constant term (the third term), ... The roots will be represented as r1 and r2.
Let us take the quadratic equation of the general form ax^2 + bx + c = 0 where a (≠ 0) is the coefficient of x^2, b the coefficient of x and c, the constant term.
Let α and β be the roots of the equation ax^2 + bx + c = 0
Now we are going to find the relations of α and β with a, b and c.
Now ax^2 + bx + c = 0
Multiplication both sides by 4a (a ≠ 0) we get
4a^2x^2 + 4abx + 4ac = 0
(2ax)^2 + 2 * 2ax * b + b^2 – b^2 + 4ac = 0
(2ax + b)^2 = b^2 - 4ac
2ax + b = ±√b^2−4ac
x = −b±√b2−4ac/2a
Therefore, the roots of (i) are −b±√b2−4ac/2a
Let α = −b+√b2−4ac/2a and β = −b-√b2−4ac/2a
Therefore,
α + β = −b+√b2−4ac/2a + −b-√b2−4ac/2a
α + β = −2b2a
α + β = -ba
α + β = -coefficient of X /coefficientof x^2
Again, αβ =−b+√b2−4ac/2a× −b-√b2−4ac/2a
αβ = (−b)^2−√(b^2−4ac)^2/ 4a^2
αβ = b^2−(b^2−4ac)/4a^2
αβ = 4ac/4a^2
αβ = ca
αβ = constant term / coefficient of x^2
Therefore, α + β = -coefficient of x / coefficient of x^2 and αβ = constant term / coefficient of x^2 represent the required relations between roots (i.e., α and β) and coefficients (i.e., a, b and c) of equation ax^2 + bx + c = 0.