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equilibrum
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Hi. I've been attempting this modulus problem from my textbook for the past hour and could not find a way to get the correct answer.
The equation x^2 -(k+2)x + 2k + 1 = 0 ,where k is a constant has two real roots α and β.
1)Express α+β and αβ in terms of k
b) if |α| = |β| , find
2)the possible values of k
3)the roots corresponding to each value of k
α+β = -b/a
αβ = c/a
b^2-4ac = 0 / D = 0 or >/< or >= / =<
Part 1 is just formula,no problem with that.
2)I presumed from the question that since the equation has two real roots(cuts at two distinct points) and/or since the modulus of alpha is equal to the modulus of beta,the roots may also be the same and therefore i applied the formula b^2 -4ac ≥ 0
(-(k+2))^2 - 4(1)(2k+1) ≥ 0
k^2-4k ≥ 0
k(k-4)≥0
By solving using quadratic inequalities,
k ≥ 4 or k ≤ 0
I referred to the answer for the possible values of k and it was 4,0,-2 . If i did a guess and check by substituting k = 4 into the equation i will get the same roots when they are in modulus form and this is also true for k = 0 . I guess this method although gives me the correct answer and proves it ,is wrong. This is because I cannot find the other possible value of k which was -2 unless i did a guess and check by going under 0 as shown in the inequality but I guess that there must be another method(as i presume that doing guess and check can yield an infinite number of solutions with decimal places etc.) . I need help on that.
Any inputs is kindly appreciated.
Homework Statement
The equation x^2 -(k+2)x + 2k + 1 = 0 ,where k is a constant has two real roots α and β.
1)Express α+β and αβ in terms of k
b) if |α| = |β| , find
2)the possible values of k
3)the roots corresponding to each value of k
Homework Equations
α+β = -b/a
αβ = c/a
b^2-4ac = 0 / D = 0 or >/< or >= / =<
The Attempt at a Solution
Part 1 is just formula,no problem with that.
2)I presumed from the question that since the equation has two real roots(cuts at two distinct points) and/or since the modulus of alpha is equal to the modulus of beta,the roots may also be the same and therefore i applied the formula b^2 -4ac ≥ 0
(-(k+2))^2 - 4(1)(2k+1) ≥ 0
k^2-4k ≥ 0
k(k-4)≥0
By solving using quadratic inequalities,
k ≥ 4 or k ≤ 0
I referred to the answer for the possible values of k and it was 4,0,-2 . If i did a guess and check by substituting k = 4 into the equation i will get the same roots when they are in modulus form and this is also true for k = 0 . I guess this method although gives me the correct answer and proves it ,is wrong. This is because I cannot find the other possible value of k which was -2 unless i did a guess and check by going under 0 as shown in the inequality but I guess that there must be another method(as i presume that doing guess and check can yield an infinite number of solutions with decimal places etc.) . I need help on that.
Any inputs is kindly appreciated.