Find q if the root of equation 3x²+qx-12=0 differ by 4. (quadratic question)?
Hello again,
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
0.► In any quadratic equation of the form:
𝑥² – 𝑆𝑥 + 𝑃 = 0
we always have the properties:
● 𝑆 will be the sum of the roots.
● 𝑃 will be the product of the roots.
2.► Thus starting from your equation:
3𝑥² + 𝑞𝑥 – 12 = 0
𝑥² + (𝑞/3)𝑥 – 4 = 0
So let 𝛼 be one of the root of this equation. The other, differing by 4, will then be: 𝛼+4.
We then have:
{ 𝑆 = 2𝛼 + 4 = -𝑞/3
{ 𝑃 = 𝛼² + 4𝛼 = -4
From last equation:
𝛼² + 4𝛼 = -4
𝛼² + 4𝛼 + 4 = 0
(𝛼 + 2)² = 0
𝛼 + 2 = 0
𝛼 = -2
From first equation:
2𝛼 + 4 = -𝑞/3
𝑞/3 = -2𝛼 – 4
𝑞 = -6𝛼 – 12
and knowing 𝛼=-2
𝑞 = 0 ◄◄◄ ANSWER
Regards,
Dragon.Jade :-)
3x² - qx + 12 = 0
Polynomial like: ax² + bx + c, where:
a = 3
b = - q
c = 12
Δ = b² - 4ac (discriminant)
x₁ = (- b - √Δ)/2a
x₂ = (- b + √Δ)/2a
x₁ - x₂ = 4
[(- b - √Δ)/2a] - [(- b + √Δ)/2a] = 4
[(- b - √Δ) - (- b + √Δ)]/2a = 4
(- b - √Δ) - (- b + √Δ) = 8a
- b - √Δ + b - √Δ = 8a
- 2√Δ = 8a
√Δ = - 4a
(√Δ)² = (- 4a)²
Δ = 16a² → recall: Δ = b² - 4ac
b² - 4ac = 16a² → recall: a = 3
b² - 12c = 144 → recall: c = 12
b² - 144 = 144
b² = 288 → recall: b = q
q² = 288
q = ± √288
q = ± 12√2
3x²+qx-12=0
r₁ = [-q + √(q² + 4•3•12)}/6 = [-q + √(q²+144)]/6
r₂ = [-q - √(q² + 4•3•12)}/6 = [-q -√(q²+144)]/6
Given r₁ - r₂ = 4
r₁ - r₂ = [-q + √(q²+144)]/6 - [-q -√(q²+144)]/6
= 2√(q²+144)/6 = 4
√(q²+144) = 12
q² + 144 = 144
q² = 0
Ans: q = 0
=========================
Verification:
3x² + (0)x - 12 = 0
x² = 4
r₁ = 2
r₂ = -2
r₁ - r₂ = 4
q could be any number
do you mean find p?
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Answers & Comments
Verified answer
Hello again,
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
0.► In any quadratic equation of the form:
𝑥² – 𝑆𝑥 + 𝑃 = 0
we always have the properties:
● 𝑆 will be the sum of the roots.
● 𝑃 will be the product of the roots.
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
2.► Thus starting from your equation:
3𝑥² + 𝑞𝑥 – 12 = 0
𝑥² + (𝑞/3)𝑥 – 4 = 0
So let 𝛼 be one of the root of this equation. The other, differing by 4, will then be: 𝛼+4.
We then have:
{ 𝑆 = 2𝛼 + 4 = -𝑞/3
{ 𝑃 = 𝛼² + 4𝛼 = -4
From last equation:
𝛼² + 4𝛼 = -4
𝛼² + 4𝛼 + 4 = 0
(𝛼 + 2)² = 0
𝛼 + 2 = 0
𝛼 = -2
𝛼 = -2
From first equation:
2𝛼 + 4 = -𝑞/3
𝑞/3 = -2𝛼 – 4
𝑞 = -6𝛼 – 12
and knowing 𝛼=-2
𝑞 = 0 ◄◄◄ ANSWER
Regards,
Dragon.Jade :-)
3x² - qx + 12 = 0
Polynomial like: ax² + bx + c, where:
a = 3
b = - q
c = 12
Δ = b² - 4ac (discriminant)
x₁ = (- b - √Δ)/2a
x₂ = (- b + √Δ)/2a
x₁ - x₂ = 4
[(- b - √Δ)/2a] - [(- b + √Δ)/2a] = 4
[(- b - √Δ) - (- b + √Δ)]/2a = 4
(- b - √Δ) - (- b + √Δ) = 8a
- b - √Δ + b - √Δ = 8a
- 2√Δ = 8a
√Δ = - 4a
(√Δ)² = (- 4a)²
Δ = 16a² → recall: Δ = b² - 4ac
b² - 4ac = 16a² → recall: a = 3
b² - 12c = 144 → recall: c = 12
b² - 144 = 144
b² = 288 → recall: b = q
q² = 288
q = ± √288
q = ± 12√2
3x²+qx-12=0
r₁ = [-q + √(q² + 4•3•12)}/6 = [-q + √(q²+144)]/6
r₂ = [-q - √(q² + 4•3•12)}/6 = [-q -√(q²+144)]/6
Given r₁ - r₂ = 4
r₁ - r₂ = [-q + √(q²+144)]/6 - [-q -√(q²+144)]/6
= 2√(q²+144)/6 = 4
√(q²+144) = 12
q² + 144 = 144
q² = 0
Ans: q = 0
=========================
Verification:
3x² + (0)x - 12 = 0
x² = 4
r₁ = 2
r₂ = -2
r₁ - r₂ = 4
q could be any number
do you mean find p?