Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Quadratic Equation and Inequalities question

2020 · 8 Jan · Shift 1 · Q22
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Mathematics
  4. /Quadratic Equation and Inequalities
  5. /2020 · 8 Jan · Shift 1 · Q22

Quadratic Equation and Inequalities question

2020 · 8 Jan · Shift 1 · Q22

JEE MainMathematicsQuadratic Equation and InequalitiesNumerical+4 / −1
The least positive value of 'a' for which the equation 2x2 + (a – 10)x + 332{{33} \over 2}233​ = 2a has real roots is
Numerical answer
View written solutionFree

Correct answer: 8

We need the least positive value of aaa such that the quadratic equation has real roots.

1. Rewrite the equation in standard quadratic form

Given: 2x2+(a−10)x+332=2a2x^2 + (a-10)x + \frac{33}{2} = 2a2x2+(a−10)x+233​=2a

Bring all terms to one side: 2x2+(a−10)x+332−2a=02x^2 + (a-10)x + \frac{33}{2} - 2a = 02x2+(a−10)x+233​−2a=0

So the quadratic is: 2x2+(a−10)x+(332−2a)=02x^2 + (a-10)x + \left(\frac{33}{2} - 2a\right)=02x2+(a−10)x+(233​−2a)=0

Here, A=2,B=a−10,C=332−2aA=2,\quad B=a-10,\quad C=\frac{33}{2}-2aA=2,B=a−10,C=233​−2a

2. Condition for real roots

For a quadratic equation to have real roots, its discriminant must satisfy: D≥0D \ge 0D≥0

So, B2−4AC≥0B^2 - 4AC \ge 0B2−4AC≥0

Substitute the values: (a−10)2−4(2)(332−2a)≥0(a-10)^2 - 4(2)\left(\frac{33}{2}-2a\right) \ge 0(a−10)2−4(2)(233​−2a)≥0

3. Simplify the discriminant

First compute: 4(2)(332−2a)=8(332−2a)=132−16a4(2)\left(\frac{33}{2}-2a\right)=8\left(\frac{33}{2}-2a\right)=132-16a4(2)(233​−2a)=8(233​−2a)=132−16a

Thus, (a−10)2−(132−16a)≥0(a-10)^2 - (132-16a) \ge 0(a−10)2−(132−16a)≥0

Expand: a2−20a+100−132+16a≥0a^2 - 20a + 100 - 132 + 16a \ge 0a2−20a+100−132+16a≥0 a2−4a−32≥0a^2 - 4a - 32 \ge 0a2−4a−32≥0

Factorize: a2−4a−32=(a−8)(a+4)a^2 - 4a - 32 = (a-8)(a+4)a2−4a−32=(a−8)(a+4)

Hence, (a−8)(a+4)≥0(a-8)(a+4) \ge 0(a−8)(a+4)≥0

4. Solve the inequality

Critical points are a=8a=8a=8 and a=−4a=-4a=−4.

So, a≤−4ora≥8a \le -4 \quad \text{or} \quad a \ge 8a≤−4ora≥8

We need the least positive value of aaa.

Therefore, 8\boxed{8}8​

5. Compare with stored answer

Stored correct answer: 888

Our derived answer is also 888, so they agree.

PreviousNext

More from Quadratic Equation and Inequalities

  • Let α=2−1+i3​​. If a=(1+α)k=0∑100​α2k and b=k=0∑100​α3k, then a and b are the roots of the quadratic equation :2020 · MCQ
  • Let S be the set of all real roots of the equation, 3x(3x – 1) + 2 = |3x – 1| + |3x – 2|. Then S :2020 · MCQ
  • The number of real roots of the equation, e4x + e3x – 4e2x + ex + 1 = 0 is :2020 · MCQ
  • Let a, b ∈ R, a e 0 be such that the equation, ax2 – 2bx + 5 = 0 has a repeated root α, which is also a root of the equation, x2 – 2bx – 10 = 0. If β is the other root of this equation, then α 2 + β 2 is…2020 · MCQ
  • The sum of the solutions of the equation ∣x​−2∣+x​(x​−4)+2=0 (x > 0) is equal to:2019 · MCQ
  • The number of integral values of m for which the equation (1 + m2 )x2 – 2(1 + 3m)x + (1 + 8m) = 0 has no real root is :2019 · MCQ
  • Let p, q ∈ R. If 2 - 3​ is a root of the quadratic equation, x2 + px + q = 0, then :2019 · MCQ
  • If m is chosen in the quadratic equation (m2 + 1) x2 – 3x + (m2 + 1)2 = 0 such that the sum of its roots is greatest, then the absolute difference of the cubes of its roots is :-2019 · MCQ