Discriminant Flashcards: Real Roots & Parameter Boundaries
Practice 40 original discriminant prompts: count distinct real roots, repair coefficient errors, interpret graph clues, and check parameter boundaries when the x² term vanishes.
このデッキについて
Count distinct real roots without solving every quadratic. These 40 discriminant flashcards give English-reading algebra learners original short decisions about signed coefficients, repeated roots, graph clues and parameter boundaries.
Practice runs in several directions: equation or discriminant sign → real-root count; a stated root count or graph position → discriminant condition; and a short parameter equation → the values that meet a root-count condition. Error-repair cards address missing coefficients, signs, zero form, and the difference between a zero discriminant and a zero root. Later cards check when the x² term vanishes: the remaining equation may be linear, a contradiction or an identity. Every prompt carries the context needed for mixed review.
The sequence introduces zero form, coefficient reading and the nonzero leading-coefficient requirement, then adds the three sign cases with short calculations between them. Reverse cues and error diagnosis lead into parameter intervals and degenerate cases. Related variants are separated by at least three other cards. All cards use the discriminant tag; the review scheduler handles long-term spacing.
Know signed arithmetic, squares and simple inequalities before starting. Coefficients and parameters are real unless a card says otherwise, and root counts mean distinct real roots. This evergreen Mathematics deck has no exam or curriculum alignment. It excludes complex-root calculations, rational-versus-irrational classification, higher-degree discriminants, full quadratic-formula drills and long proofs. Arbitrary reversals from a root count to unique coefficients are excluded because that information does not determine a unique equation.
The discriminant identity and quadratic-root formula were fact-checked using NIST DLMF §1.11. All examples, wording and organization were independently created from common algebra and checked with exact arithmetic, completing-square reasoning, factorization or substitution. No textbook exercises, competitor cards, exam questions, source prose or diagrams were copied or adapted.
AI tools assisted with drafting and the original decorative cover. Every final front and back received author review, with an independent readiness review before publication; this does not claim learner testing. The CC0 dedication covers original wording, invented examples, organization, metadata and generated cover to the extent applicable rights exist. Mathematical facts and cited materials retain their own status. This is independent study practice, with no affiliation to or endorsement by NIST or any course or examination provider.
このデッキのカード
カード 1
質問
For real coefficients in ax² + bx + c = 0, with a ≠ 0, what is the discriminant?
回答
D = b² − 4ac. Its sign tells you the number of distinct real roots.
カード 2
質問
Rewrite x² = 5x + 1 in zero form before using the discriminant.
回答
x² − 5x − 1 = 0. Use a = 1, b = −5 and c = −1.
カード 3
質問
In −2x² + 7x − 4 = 0, what are a, b and c?
回答
a = −2, b = 7, c = −4. Keep the signs attached to the coefficients.
カード 4
質問
Before using the quadratic discriminant on ax² + bx + c = 0, which coefficient must be nonzero?
回答
a ≠ 0. If a = 0, solve bx + c = 0 separately; the equation is no longer quadratic.
カード 5
質問
A real quadratic has D > 0. How many distinct real roots?
回答
Two distinct real roots. The two square-root choices in the quadratic formula give different real values.
カード 6
質問
Find the discriminant of 3x² − 2x − 4 = 0.
回答
52
D = (−2)² − 4(3)(−4) = 4 + 48 = 52.
カード 7
質問
In 4x² + 9 = 0, what value of b belongs in D = b² − 4ac?
回答
b = 0. There is no x term; c = 9 is the constant coefficient.
カード 8
質問
A real quadratic has a negative x² coefficient. Does that alone determine its number of real roots?
回答
No. The parabola opens downward, but D can be positive, zero or negative.
カード 9
質問
A real quadratic has D = 0. How many distinct real roots?
回答
One distinct real root, repeated twice. Its value is −b/(2a).
カード 10
質問
How many distinct real roots does 6x² + 5x − 6 = 0 have?
回答
Two. D = 5² − 4(6)(−6) = 169 > 0. You do not need to solve for the roots to count them.
カード 11
質問
For b = −5, a student uses b² = −25 in the discriminant. What should replace −25?
回答
25
Square the whole signed coefficient: (−5)² = 25.
カード 12
質問
For x² + 4x = 2, a student uses c = 2. What is the correct discriminant?
回答
24
First write x² + 4x − 2 = 0, so c = −2 and D = 4² − 4(1)(−2) = 24.
カード 13
質問
A real quadratic has D < 0. How many real roots?
回答
None. A negative discriminant has no real square root.
カード 14
質問
How many distinct real roots does 4x² + 12x + 9 = 0 have?
回答
One. D = 12² − 4(4)(9) = 0. The equation is (2x + 3)² = 0, so its repeated root is −3/2.
カード 15
質問
How many distinct real roots does x² − 7x = 0 have?
回答
Two. D = (−7)² − 4(1)(0) = 49 > 0. Factoring gives x(x − 7) = 0, with roots 0 and 7.
カード 16
質問
What discriminant condition is necessary and sufficient for a real quadratic to have two distinct real roots?
回答
D > 0. The condition assumes the x² coefficient is nonzero.
カード 17
質問
How many real roots does 2x² + 4x + 5 = 0 have?
回答
None. D = 4² − 4(2)(5) = −24 < 0.
カード 18
質問
A real quadratic graph touches the x-axis at exactly one point. What is its discriminant?
回答
D = 0. The touching point corresponds to a repeated real root.
カード 19
質問
How many distinct real roots does −3x² + 2x + 2 = 0 have?
回答
Two. D = 2² − 4(−3)(2) = 28 > 0. A negative leading coefficient does not prevent real roots.
カード 20
質問
For x² + 5 = 0, a student uses b = 5 and c = 0. What is the correct discriminant?
回答
−20. The coefficients are a = 1, b = 0 and c = 5, so D = 0² − 4(1)(5) = −20.
カード 21
質問
What discriminant condition is necessary and sufficient for a real quadratic to have no real roots?
回答
D < 0. The coefficients are real and the x² coefficient is nonzero.
カード 22
質問
For which real k does x² − 6x + k = 0 have a repeated root?
回答
k = 9. D = 36 − 4k = 0. At that value the equation is (x − 3)² = 0.
カード 23
質問
Does D = 0 mean the root is zero?
回答
No. It means the two roots coincide. For (3x − 2)² = 0, the repeated root is 2/3, while D = 0.
カード 24
質問
A real quadratic equation is multiplied throughout by a nonzero real λ. How does its discriminant change?
回答
It becomes λ²D. Since λ² > 0, the sign and number of distinct real roots stay the same. Multiplying by zero would turn the equation into 0 = 0.
カード 25
質問
An upward-opening real quadratic graph has its vertex strictly below the x-axis. What is the sign of D?
回答
Positive: D > 0. The graph crosses the x-axis twice. The vertex must be strictly below, not on, the axis.
カード 26
質問
For which real k does x² + 8x + k = 0 have two distinct real roots?
回答
k < 16. D = 64 − 4k must be positive. At k = 16 there is only one distinct real root, so exclude the boundary.
カード 27
質問
How many distinct real roots does −2x² + 8x − 8 = 0 have?
回答
One. D = 8² − 4(−2)(−8) = 0. The equation is −2(x − 2)² = 0, so the repeated root is 2.
カード 28
質問
For which real k is (k − 2)x² + 3x + 1 = 0 a quadratic equation?
回答
k ≠ 2. The x² coefficient is k − 2, which must be nonzero.
カード 29
質問
For which real t does x² + 2tx + 9 = 0 have no real roots?
回答
−3 < t < 3. D = 4t² − 36 < 0 gives t² < 9. At t = −3 or 3 there is a repeated real root, so exclude both endpoints.
カード 30
質問
For which real k does x² + 10x + k = 0 have no real roots?
回答
k > 25. D = 100 − 4k must be negative. At k = 25 the repeated root is −5, so exclude that boundary.
カード 31
質問
For which real k does x² + kx − 4 = 0 have two distinct real roots?
回答
Every real k. D = k² + 16 is always positive, and the leading coefficient stays 1.
カード 32
質問
At k = 2, how many real solutions does (k − 2)x² + 3x + 1 = 0 have?
回答
One: x = −1/3. At k = 2 the x² term vanishes and the equation becomes 3x + 1 = 0; use the linear equation.
カード 33
質問
For which real k does kx² + 2x + 1 = 0 have exactly one distinct real solution?
回答
k = 0 or k = 1. At k = 0 the equation is linear, with x = −1/2. For k ≠ 0, D = 4 − 4k must be zero, giving k = 1 and repeated root −1.
カード 34
質問
For which real t does x² + 2tx + 9 = 0 have two distinct real roots?
回答
t < −3 or t > 3. D = 4t² − 36 > 0 gives t² > 9. Both boundary values give a repeated root and are excluded.
カード 35
質問
For which real k does kx² + 6x + 2 = 0 have no real solutions?
回答
k > 9/2. For k ≠ 0, D = 36 − 8k < 0 gives this interval. At k = 0 the linear equation 6x + 2 = 0 has one solution; at k = 9/2 there is a repeated root.
カード 36
質問
At k = 4, how many real solutions does (k − 4)x² + (k − 4)x + 1 = 0 have?
回答
None. Both variable terms vanish, leaving 1 = 0, which is false for every x. A zero leading coefficient does not always leave a solvable linear equation.
カード 37
質問
At k = 0, how many real solutions does kx² + kx = 0 have?
回答
Infinitely many: every real x. The equation becomes 0 = 0. Do not apply the quadratic D = 0 rule when the leading coefficient is zero.
カード 38
質問
How many distinct real roots does x² = 0 have?
回答
One: x = 0. D = 0; zero is a repeated root, counted once when counting distinct roots.
カード 39
質問
Do x² − 2x − 2 = 0 and −3x² + 6x + 6 = 0 have different numbers of distinct real roots?
回答
No; each has two. Their discriminants are 12 and 108, both positive. The second equation is the first multiplied by −3, so even the roots themselves are unchanged.
カード 40
質問
For which real k does (k − 4)x² + (k − 4)x + 1 = 0 have two distinct real roots?
回答
k < 4 or k > 8. For k ≠ 4, D = (k − 4)(k − 8) must be positive. At k = 4 the equation is 1 = 0; at k = 8 it has a repeated root. Exclude both boundaries.
40枚のカード
Discriminant Flashcards: Real Roots & Parameter Boundaries
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