Home
Class 11
MATHS
(i) Find the values of 'a' for which the...

(i) Find the values of 'a' for which the expression
`x^(2)-(3a-1)x+2a^(2)+2a-11` is always positive
(ii) If `x^(2)+4ax+2 gt0` for all values of x, then a lies in the interval.
(a) `(-2,4)`
(b) (1,2)
(c) `(-sqrt(2),sqrt(2))`
(d) `(-(1)/(sqrt(2)),(1)/(sqrt(2)))`
(e) (-4,2).

Text Solution

AI Generated Solution

The correct Answer is:
To solve the given problem step by step, we will break it down into two parts as per the question. ### Part (i): Finding values of 'a' for which the expression is always positive We need to determine the values of \( a \) such that the expression \[ x^2 - (3a - 1)x + (2a^2 + 2a - 11) \] is always positive. For a quadratic expression \( ax^2 + bx + c \) to be always positive, its discriminant \( D \) must be less than zero. 1. **Identify the coefficients**: - Here, \( a = 1 \) (coefficient of \( x^2 \)), - \( b = -(3a - 1) = -3a + 1 \), - \( c = 2a^2 + 2a - 11 \). 2. **Calculate the discriminant**: \[ D = b^2 - 4ac \] Substituting the values: \[ D = (-3a + 1)^2 - 4(1)(2a^2 + 2a - 11) \] 3. **Expand the discriminant**: \[ D = (9a^2 - 6a + 1) - (8a^2 + 8a - 44) \] Simplifying this: \[ D = 9a^2 - 6a + 1 - 8a^2 - 8a + 44 \] \[ D = a^2 - 14a + 45 \] 4. **Set the discriminant less than zero**: \[ a^2 - 14a + 45 < 0 \] 5. **Factor the quadratic**: We can factor this as: \[ (a - 5)(a - 9) < 0 \] 6. **Find the intervals**: The roots of the equation are \( a = 5 \) and \( a = 9 \). The quadratic will be negative between the roots: \[ 5 < a < 9 \] ### Conclusion for Part (i): The values of \( a \) for which the expression is always positive are: \[ a \in (5, 9) \] --- ### Part (ii): Finding the interval for \( a \) such that \( x^2 + 4ax + 2 > 0 \) for all \( x \) 1. **Identify the coefficients**: - Here, \( a = 1 \), - \( b = 4a \), - \( c = 2 \). 2. **Calculate the discriminant**: \[ D = (4a)^2 - 4(1)(2) \] \[ D = 16a^2 - 8 \] 3. **Set the discriminant less than zero**: \[ 16a^2 - 8 < 0 \] 4. **Simplify the inequality**: \[ 16a^2 < 8 \] \[ 2a^2 < 1 \] \[ a^2 < \frac{1}{2} \] 5. **Find the interval for \( a \)**: Taking square roots: \[ -\frac{1}{\sqrt{2}} < a < \frac{1}{\sqrt{2}} \] ### Conclusion for Part (ii): The values of \( a \) for which \( x^2 + 4ax + 2 > 0 \) for all \( x \) are: \[ a \in \left(-\frac{1}{\sqrt{2}}, \frac{1}{\sqrt{2}}\right) \] ---
Promotional Banner

Topper's Solved these Questions

  • QUADRATIC EQUATIONS

    ICSE|Exercise CHAPTER TEST|24 Videos
  • QUADRATIC EQUATIONS

    ICSE|Exercise EXERCISE 10 (e)|4 Videos
  • PROPERTIES OF TRIANGLE

    ICSE|Exercise EXERCISE 7|38 Videos
  • RELATION AND FUNCTIONS

    ICSE|Exercise MULTIPLE CHOICE QUESTIONS (Choose the correct answer from the given four options in questions)|32 Videos

Similar Questions

Explore conceptually related problems

If f(x)=(1)/(sqrt(x+2sqrt(2x-4)))+(1)/(sqrt(x-2sqrt(2x-4))) for xgt2 then find f(11).

lim_(xrarr0) (sqrt(x+1)+sqrt(x+4)-3)/(sqrt(x+2)-sqrt2)

Differentiate sin^(-1)(4xsqrt(1-4x^(2)))w.r.t.sqrt(1-4x^(2)) , if x in(-(1)/(2sqrt2),(1)/(2sqrt2))

Differentiate sin^(-1)(4xsqrt(1-4x^(2)))w.r.t.sqrt(1-4x^(2)) , if x in(-(1)/(2sqrt2),(1)/(2sqrt2))

Differentiate sin^(-1)(4xsqrt(1-4x^(2)))w.r.t.sqrt(1-4x^(2)) , if x in(-(1)/(2sqrt2),(1)/(2sqrt2))

If x=(sqrt(2a+1)+sqrt(2a-1))/(sqrt(2a+1)-sqrt(2a-1)) , prove that x^(2)-4ax+1=0

If 4\ cos^(-1)x+sin^(-1)x=pi , then the value of x is (a) 3/2 (b) 1/(sqrt(2)) (c) (sqrt(3))/2 (d) 2/(sqrt(3))

lim_(x to 0) (sin^(2) x)/(sqrt(2)-sqrt(1+cos x))= (A) sqrt(2) (B) 2 (C) 4 (D) 4sqrt(2)

If two different tangents of y^2=4x are the normals to x^2=4b y , then (a) |b|>1/(2sqrt(2)) (b) |b| 1/(sqrt(2)) (d) |b|<1/(sqrt(2))

The value of lim_(xto2a)(sqrt(x-2a)+sqrt(x)-sqrt(2a))/(sqrt(x^2-4a^2)) is