Nature of Roots

Correct answer: A. D < 0, no real roots

Explanation: Here, \(a=5\), \(b=2\), and \(c=1\). Thus, the discriminant is \(D=b^2-4ac=2^2-4(5)(1)=4-20=-16\), so \(D<0\). A negative discriminant means that the quadratic equation has no real roots; its roots are complex conjugates. Option B would be correct only if \(D=0\). Exam tip: remember that \(D<0\), \(D=0\), and \(D>0\) correspond respectively to no real roots, equal real roots, and distinct real roots.

Correct answer: A. Two real and equal roots (D=0)

Explanation: When a parabola touches the x-axis at exactly one point, the quadratic has one repeated real root. Hence, the discriminant (D=b^2-4ac=0), and the two roots are real and equal. If (D>0), the graph cuts the x-axis at two points, so option B is incorrect. Exam tip: touching means (D=0), cutting means (D>0), and staying away means (D<0).

Correct answer: A. Two real and distinct roots \(D>0\)

Explanation: Each intersection of the parabola with the x-axis represents one real root of the corresponding quadratic equation. Two distinct intersections therefore indicate two real and distinct roots, so the discriminant is \(D>0\). The condition \(D=0\) applies only when the graph touches the x-axis at one point. Exam tip: Use the number of x-intercepts to identify the nature of the roots quickly.

Correct answer: A. No real roots, \(D<0\)

Explanation: The points where the parabola intersects the x-axis represent the real roots of the quadratic equation. If it neither intersects nor touches the x-axis, there is no real intercept; therefore, the discriminant satisfies \(D<0\), and the equation has no real roots. In contrast, touching the x-axis would give \(D=0\).

Correct answer: A. (8)

Explanation: For equal roots (D=0), so ((-8)^2-4(2)c=0) gives (c=8). Be careful with signs while substituting coefficients.

Correct answer: A. \(m=4\) or \(m=-4\)

Explanation: For equal roots, the discriminant \(D=b^2-4ac\) must be zero. Here, \(a=4\), \(b=m\), and \(c=1\), so \(D=m^2-16=0\). Therefore, \(m^2=16\), giving \(m=4\) or \(m=-4\). Choosing only \(m=4\) is incomplete because the negative value also produces equal roots. Exam tip: For equal-root questions, set \(b^2-4ac=0\) directly.

Correct answer: A. 4

Explanation: For equal roots, the discriminant \(D=b^2-4ac\) must be zero. Here, \(a=p\), \(b=4\), and \(c=1\), so \(D=4^2-4(p)(1)=0\), giving \(16-4p=0\) and hence \(p=4\). Option B has the wrong sign, while \(p=4\) also satisfies \(p\neq 0\), keeping the equation quadratic. Exam tip: For equal roots, immediately use \(D=0\).

Correct answer: A. \(k\leq 0\) या \(k\geq 3\)

Explanation: Here \(a=3\), \(b=2k\), and \(c=k\). Therefore, the discriminant is \(D=b^2-4ac=(2k)^2-4(3)(k)=4k(k-3)\). For real roots, \(D\geq 0\), so \(k(k-3)\geq 0\), which gives \(k\leq 0\) or \(k\geq 3\). In option B, the discriminant is negative, so the roots are not real. Exam tip: For questions about real roots, begin by applying \(D\geq 0\).

Correct answer: A. 9

Explanation: For equal roots, the discriminant \(D=b^2-4ac\) must be zero. Here, \(a=k\), \(b=-6\), and \(c=1\), so \(D=(-6)^2-4(k)(1)=0\). Thus, \(36-4k=0\), giving \(k=9\). The value 6 does not make the discriminant zero. Exam tip: For equal roots of a quadratic equation, set \(D=0\).

Correct answer: A. \(-5<k<3\)

Explanation: A quadratic equation has no real roots when its discriminant satisfies \(D<0\). Here, \(a=1\), \(b=-(k+1)\), and \(c=4\), so \(D=(k+1)^2-16\). Thus, \((k+1)^2<16\), which gives \(-4<k+1<4\), and hence \(-5<k<3\). Therefore, option A is correct. At the boundary values \(k=-5\) and \(k=3\), \(D=0\), so the equation has two equal real roots rather than no real roots. Exam tip: for ‘no real roots’, always use the condition \(D<0\).

Correct answer: A. \(k>-frac{1}{2}\)

Explanation: Here, \(a=1\), \(b=2(k+1)\), and \(c=k^2\). Therefore, the discriminant is \(D=b^2-4ac=4(k+1)^2-4k^2=4(2k+1)\). Two distinct real roots require \(D>0\), so \(4(2k+1)>0\), which gives \(k>-rac{1}{2}\). At \(k=-\frac{1}{2}\), \(D=0\), so the roots are equal rather than distinct. Exam tip: use \(D>0\) specifically for two distinct real roots.

Correct answer: A. The student has misunderstood the discriminant; \(D=-16<0\), so there are no real roots.

Explanation: Here \(a=1, b=-2, c=5\), so \(D=b^2-4ac=4-20=-16\). A negative discriminant means there are no real roots. In exams, evaluate the complete \(b^2-4ac\), not \(b^2\) alone.

Correct answer: A. Two real, rational and distinct roots

Explanation: The discriminant D = 49 is positive and a perfect square. Since D > 0, the roots are real and distinct; because D is a perfect square, the roots are rational. Therefore, option A is correct. The roots would be equal only when D = 0, so option B is incorrect. Exam tip: If D > 0 and is a perfect square, the roots are real, rational, and distinct.

Correct answer: A. Two real irrational and distinct

Explanation: For a quadratic equation, D = b² − 4ac. Since D = 12 is positive, the roots are real and distinct. Also, 12 is not a perfect square and the coefficients are rational, so the roots are irrational. Hence, option A is correct. Exam tip: D > 0 gives distinct real roots, D = 0 gives equal roots, and D < 0 gives no real roots.

Correct answer: A. \(b^2-4ac=0\)

Explanation: When the discriminant \(D=b^2-4ac\) is zero, \(\sqrt{D}=0\) in \(\frac{-b\pm\sqrt{D}}{2a}\), so both roots are equal. For \(D>0\), the roots are distinct. Exam tip: equal roots always mean \(D=0\).

Correct answer: A. Both the assertion and the reason are correct, and the reason is the correct explanation of the assertion

Explanation: Here, \(a=1\), \(b=-10\), and \(c=25\). Therefore, the discriminant is \(D=b^2-4ac=(-10)^2-4(1)(25)=100-100=0\). For a quadratic equation, \(D=0\) means that the two roots are equal. In fact, \(x^2-10x+25=(x-5)^2\), so both roots are \(5\). Hence, both the assertion and the reason are correct, and the reason correctly explains the assertion. Exam tip: Calculate \(D\) first to determine the nature of the roots.

Correct answer: A. -8

Explanation: For a quadratic equation \(ax^2+bx+c=0\), the discriminant is \(D=b^2-4ac\). Here, \(a=1\), \(b=2\), and \(c=3\), so \(D=2^2-4(1)(3)=4-12=-8\). The value 16 results from using the incorrect formula \(b^2+4ac\). Exam tip: remember the discriminant formula as \(b^2-4ac\).

Correct answer: A. Two real and equal roots (D = 0)

Explanation: Here, a = 9, b = 12, and c = 4. Therefore, the discriminant is D = b² − 4ac = 12² − 4 × 9 × 4 = 144 − 144 = 0. Hence, the roots are real and equal. In fact, 9x² + 12x + 4 = (3x + 2)², so the repeated root is x = −2/3. Option B would require D > 0, but the discriminant here is zero. Exam tip: For a quadratic equation, D = 0 indicates two equal real roots.

Correct answer: A. No real roots \(D=-136\)

Explanation: Here, \(a=7\), \(b=-2\), and \(c=5\). Therefore, the discriminant is \(D=b^2-4ac=(-2)^2-4(7)(5)=4-140=-136\). Since \(D<0\), the equation has no real roots. Option C results from taking the sign of the discriminant incorrectly. In an exam, calculate \(D\) first and then check its sign to determine the nature of the roots.

Correct answer: A. Two real, rational and distinct roots

Explanation: Here, \(a=2\), \(b=-7\), and \(c=3\). Therefore, the discriminant is \(D=b^2-4ac=(-7)^2-4(2)(3)=25\). Since \(D>0\), the roots are real and distinct; since \(D=25\) is a perfect square, they are also rational. In fact, the roots are \(3\) and \(\frac{1}{2}\). Hence, option A is correct. Exam tip: \(D>0\) indicates distinct real roots, while a perfect-square discriminant indicates rational roots.

Correct answer: A. Two real, rational and distinct roots \(D=49\)

Explanation: Here, \(a=6, b=-1, c=-2\), so the discriminant is \(D=b^2-4ac=(-1)^2-4(6)(-2)=49\). Since \(D\) is positive and a perfect square, the roots are real, rational, and distinct. Option B would require \(D=0\), while the value \(D=7\) in option D is incorrect. Exam tip: If \(D>0\) and is a perfect square, the roots are rational and distinct.

Correct answer: A. No real roots; \\(D=-64\\)

Explanation: For a quadratic equation \\(ax^2+bx+c=0\\), the discriminant is \\(D=b^2-4ac\\). Here, \\(a=4,b=4,c=5\\), so \\(D=4^2-4(4)(5)=16-80=-64\\). Since \\(D<0\\), the equation has no real roots. The roots are real and equal only when \\(D=0\\), so option B is not correct. Exam tip: determine the nature of roots by checking the sign of the discriminant first.

Correct answer: A. D = 9; two real, rational and distinct roots

Explanation: For a quadratic equation \(ax^2+bx+c=0\), the discriminant is \(D=b^2-4ac\). Here, \(a=1, b=7, c=10\), so \(D=7^2-4(1)(10)=49-40=9\). Since \(D\) is positive and a perfect square, the roots are real, rational, and distinct; in fact, they are \(-5\) and \(-2\). Therefore, option A is correct. Exam tip: \(D>0\) gives distinct real roots, and a perfect-square discriminant makes those roots rational.

Correct answer: A. Two real and equal roots \(D=0\)

Explanation: Here, \(a=3\), \(b=-6\), and \(c=3\). Therefore, the discriminant is \(D=b^2-4ac=(-6)^2-4(3)(3)=36-36=0\). Hence, the roots are real and equal. In fact, the equation can be written as \(3(x-1)^2=0\), giving the repeated root \(x=1\). Option B is incorrect because its discriminant value is wrong. Exam tip: When \(D=0\), the roots are always real and equal.

Correct answer: A. \(x^2-6x+9=0\)

Explanation: A quadratic equation \(ax^2+bx+c=0\) has two real and equal roots when its discriminant \(D=b^2-4ac\) is zero. For option (A), \(a=1, b=-6, c=9\), so \(D=(-6)^2-4(1)(9)=36-36=0\). Hence its roots are equal, namely \(x=3,3\). Options (B) and (D) have discriminants 4 and 16, respectively, so their roots are distinct; option (C) has discriminant \(-4\), so its roots are not real. Exam tip: For equal roots, check directly whether \(D=0\).