If the sum of the roots of quadratic equation is ‘3’ and t...
Solution:
Given that the sum of the roots of the quadratic equation is 3 and the sum of the cubes of the roots is 7.
Let the roots of the quadratic equation be α and β.
According to the problem,
α + β = 3
α3 + β3 = 7
We know that,
α3 + β3 = (α + β) (α2 - αβ + β2)
Substituting the values from the given equations,
7 = 3 (α2 - αβ + β2)
α2 - αβ + β2 = 7/3
Now, we also know that the sum of the roots of the quadratic equation is given by
α + β = -b/a
where a and b are the coefficients of x2 and x in the quadratic equation.
Substituting the values from the given equation,
α + β = -(-b/a) = b/a
b/a = 3
b = 3a
We need to find the quadratic equation. Let the quadratic equation be
ax2 + bx + c = 0
We know that the sum of the roots of the quadratic equation is given by
α + β = -b/a
Substituting the values of b and a, we get
α + β = -3a/a = -3
α + β + 3 = 0
We also know that the sum of the product of the roots taken two at a time is given by
αβ = c/a
Substituting the values of a and b, we get
αβ = c/a = 1/3
αβ - c/a = 0
Multiplying both sides by 3a, we get
3αβ - 3c = 0
αβ = c/3
Substituting the values of αβ and α + β in the equation α2 - αβ + β2 = 7/3, we get
α2 - (c/3) + β2 = 7/3
Multiplying both sides by 3, we get
3α2 - c + 3β2 = 7
We also know that
α2 + β2 = (α + β)2 - 2αβ
Substituting the values of α + β and αβ, we get
α2 + β2 = 32 - 2(c/3)
3α2 + 3β2 = 9 - 2c
Adding this equation to the equation 3α2 - c + 3β2 = 7, we get
6α2 + 6β2 - c = 16
Substituting the value of c in this equation, we get
6α2 + 6β2 - (αβ) = 16/3
Multiplying both sides by 3, we get
18α2 + 18β2 - αβ = 16
Substituting the values of αβ and α + β in the equation α2 - αβ + β2 = 7/3, we get
6α2 + 6β2 - (α2 + β2 - (7/3)) = 16
5α2 + 5β2 = 31/3
Multiplying both sides by 3, we get
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