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Applications of the Discriminant>
Applications of the Discriminant 1Applications of the Discriminant 1
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Question 1 of 7
1. Question
Using the discriminant, find the nature of the roots of the function:5x2-6x+4=05x2−6x+4=0- 1.
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One real root -
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Two real roots
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Nature of the Roots Discriminant (ΔΔ) Two real roots ΔΔ>>00 One real root Δ=0Δ=0 No real roots ΔΔ<<00 Discriminant Formula
Δ=b2−4acΔ=b2−4acFirst, compute for the discriminant5x2-6x+4=05x2−6x+4=0a=5a=5 b=-6b=−6 c=4c=4ΔΔ == b2−4acb2−4ac Discriminant Formula == (−6)2−4(5)(4)(−6)2−4(5)(4) Substitute values == 36-8036−80 == -44−44 This is a negative value, which means ΔΔ<<00Therefore, the function has No real rootsNo real roots -
Question 2 of 7
2. Question
Identify which values of kk will make the function below have one real rootx2-(k-8)x+4=0x2−(k−8)x+4=0-
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Nature of the Roots Discriminant (ΔΔ) Two real roots ΔΔ>>00 One real root Δ=0Δ=0 No real roots ΔΔ<<00 Discriminant Formula
Δ=b2−4acΔ=b2−4acFirst, compute for the discriminantx2-(k-8)x+4=0x2−(k−8)x+4=0a=1a=1 b=k-8b=k−8 c=4c=4ΔΔ == b2−4acb2−4ac Discriminant Formula == (k−8)2−4(1)(4)(k−8)2−4(1)(4) Substitute values == k2-16k+64-16k2−16k+64−16 == k2-16k+48k2−16k+48 Remember that for a function to have one real root, ΔΔ==00Substitute the ΔΔ computed previously, and then solve for kkΔΔ == 00 k2-16k+48k2−16k+48 == 00 [insert cross method with two kk’s on the right and -4−4 & -12−12 on the left](k-4)(k-12)(k−4)(k−12) == 00 k=4,12k=4,12 k=4,12k=4,12 -
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Question 3 of 7
3. Question
Identify which values of kk will make the function below have two real rootsx2-3kx+9=0x2−3kx+9=0-
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Nature of the Roots Discriminant (ΔΔ) Two real roots ΔΔ>>00 One real root Δ=0Δ=0 No real roots ΔΔ<<00 Discriminant Formula
Δ=b2−4acΔ=b2−4acFirst, compute for the discriminantx2-3kx+9=0x2−3kx+9=0a=1a=1 b=-3kb=−3k c=9c=9ΔΔ == b2−4acb2−4ac Discriminant Formula == (−3k)2−4(1)(9)(−3k)2−4(1)(9) Substitute values == 9k2-369k2−36 Remember that for a function to have two real roots, ΔΔ>>00Substitute the ΔΔ computed previously, and then solve for kkΔΔ >> 00 9k2-369k2−36 >> 00 9(k2-4)9(k2−4) >> 00 9(k-2)(k+2)9(k−2)(k+2) >> 00 k=2k=2 k=-2k=−2 To determine which region around k=-2k=−2 and k=2k=2 would be included, plot these points and make a rough sketch of 9k2-369k2−36Replace the xx axis with kk axis and draw an upward parabola since 99 is positiveRemember that ΔΔ must be positiveTherefore, kk<<-2−2 and kk>>22kk<<-2−2 and kk>>22 -
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Question 4 of 7
4. Question
Identify which values of kk will make the function below have real rootsx2+(k+2)x+4=0x2+(k+2)x+4=0-
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Nature of the Roots Discriminant (ΔΔ) Two real roots ΔΔ>>00 One real root Δ=0Δ=0 No real roots ΔΔ<<00 Discriminant Formula
Δ=b2−4acΔ=b2−4acFirst, compute for the discriminantx2+(k+2)x+4=0x2+(k+2)x+4=0a=1a=1 b=k+2b=k+2 c=4c=4ΔΔ == b2−4acb2−4ac Discriminant Formula == (k+2)2−4(1)(4)(k+2)2−4(1)(4) Substitute values == k2+4k+4-16k2+4k+4−16 == k2+4k-12k2+4k−12 A function that has real roots can have either one or two real roots, hence ΔΔ≥≥00Substitute the ΔΔ computed previously, and then solve for kkΔΔ ≥≥ 00 k2+4k-12k2+4k−12 ≥≥ 00 (k+6)(k-2)(k+6)(k−2) ≥≥ 00 k=-6k=−6 k=2k=2 To determine which region around k=-6k=−6 and k=2k=2 would be included, plot these points and make a rough sketch of k2+4k-12k2+4k−12Replace the xx axis with kk axis and draw an upward parabola since 11 is positiveRemember that ΔΔ must be positiveTherefore, kk≤≤-6−6 and kk≥≥22kk≤≤-6−6 and kk≥≥22 -
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Question 5 of 7
5. Question
Identify which values of kk will make the function below have one real rootkx2-4x+k=0kx2−4x+k=0-
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Nature of the Roots Discriminant (ΔΔ) Two real roots ΔΔ>>00 One real root Δ=0Δ=0 No real roots ΔΔ<<00 Discriminant Formula
Δ=b2−4acΔ=b2−4acFirst, compute for the discriminantkx2-4x+k=0kx2−4x+k=0a=ka=k b=-4b=−4 c=kc=kΔΔ == b2−4acb2−4ac Discriminant Formula == (−4)2−4(k)(k)(−4)2−4(k)(k) Substitute values == 16-4k216−4k2 Remember that the function must have one real root, hence Δ=0Δ=0Substitute the ΔΔ computed previously, and then solve for kkΔΔ == 00 16-4k216−4k2 == 00 4(4-k2)4(4−k2) == 00 4(2-k)(2+k)4(2−k)(2+k) == 00 k=-2k=−2 k=2k=2 k=-2,2k=−2,2 -
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Question 6 of 7
6. Question
Identify which values of mm will make the function below have one real root2x2+mx+8=02x2+mx+8=0-
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Hint
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Chapters- Chapters
Nature of the Roots Discriminant (ΔΔ) Two real roots ΔΔ>>00 One real root Δ=0Δ=0 No real roots ΔΔ<<00 Discriminant Formula
Δ=b2−4acΔ=b2−4acFirst, compute for the discriminant2x2+mx+8=02x2+mx+8=0a=2a=2 b=mb=m c=8c=8ΔΔ == b2−4acb2−4ac Discriminant Formula == m2−4(2)(8)m2−4(2)(8) Substitute values == m2-64m2−64 Remember that the function must have one real root, hence Δ=0Δ=0Substitute the ΔΔ computed previously, and then solve for mmΔΔ == 00 m2-64m2−64 == 00 (m+8)(m-8)(m+8)(m−8) == 00 m=-8,8m=−8,8 m=-8,8m=−8,8 -
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Question 7 of 7
7. Question
For what value of kk will the line y=3x-ky=3x−k be tangent to the parabola of y=2x2-x+3y=2x2−x+3- k=k= (-1)
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Nature of the Roots Discriminant (ΔΔ) Two real roots ΔΔ>>00 One real root Δ=0Δ=0 No real roots ΔΔ<<00 Discriminant Formula
Δ=b2−4acΔ=b2−4acEquate the two functions and solve for kk in such a way that the discriminant (ΔΔ) will be 00First, equate the two functions to create a single equationy=2x2-x+3y=2x2−x+3y=3x-ky=3x−k2x2-x+32x2−x+3 == 3x-k3x−k 2x2-x+3-3x+k2x2−x+3−3x+k == 00 Move all values to the left 2x2-4x+3+k2x2−4x+3+k == 00 Next, compute for the discriminant2x2-4x+3+k2x2−4x+3+ka=2a=2 b=-4b=−4 c=3+kc=3+kΔΔ == b2−4acb2−4ac Discriminant Formula == (−4)2−4(2)(3+k)(−4)2−4(2)(3+k) Substitute values == 16-24-8k16−24−8k == -8-8k−8−8k Remember that the line must be a tangent to the parabola which means they meet at one point and that the previous equation must have one root, hence Δ=0Δ=0Substitute the ΔΔ computed previously, and then solve for kΔ = 0 -8-8k = 0 -8-8k +8 = 0 +8 Add 8 to both sides -8k = 8 -8k÷(-8) = 8÷(-8) Divide both sides by -8 k = -1 k=-1
Quizzes
- Sum & Product of Roots 1
- Sum & Product of Roots 2
- Sum & Product of Roots 3
- Sum & Product of Roots 4
- Solving Equations by Factoring 1
- Solving Equations Using the Quadratic Formula
- Completing the Square 1
- Completing the Square 2
- Intro to Quadratic Functions (Parabolas) 1
- Intro to Quadratic Functions (Parabolas) 2
- Intro to Quadratic Functions (Parabolas) 3
- Graph Quadratic Functions in Standard Form 1
- Graph Quadratic Functions in Standard Form 2
- Graph Quadratic Functions by Completing the Square
- Graph Quadratic Functions in Vertex Form
- Write a Quadratic Equation from the Graph
- Write a Quadratic Equation Given the Vertex and Another Point
- Quadratic Inequalities 1
- Quadratic Inequalities 2
- Quadratics Word Problems 1
- Quadratics Word Problems 2
- Quadratic Identities
- Graphing Quadratics Using the Discriminant
- Positive and Negative Definite
- Applications of the Discriminant 1
- Applications of the Discriminant 2
- Solving Reducible Equations