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Question

If the roots of the equation $(4 + m)x^2 + (m + 1)x + 1 = 0$ are equal, then find the values of m.

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
m = 5, -3

Solving for m with Equal Roots

The problem requires finding the value(s) of m for the quadratic equation $(4 + m)x^2 + (m + 1)x + 1 = 0$ when its roots are equal.

Condition for Equal Roots

A quadratic equation $ax^2 + bx + c = 0$ has equal roots if its discriminant, $D$, is equal to zero. The discriminant is calculated as:

$D = b^2 - 4ac$

For the given equation, we identify the coefficients:

  • $a = 4 + m$
  • $b = m + 1$
  • $c = 1$

Applying the Discriminant Condition

Setting the discriminant to zero:

$D = (m + 1)^2 - 4(4 + m)(1) = 0$

Calculating Values of m

Now, we solve the equation for m:

  1. Expand the terms: $(m^2 + 2m + 1) - (16 + 4m) = 0$
  2. Simplify the equation: $m^2 + 2m + 1 - 16 - 4m = 0$
  3. Combine like terms: $m^2 - 2m - 15 = 0$
  4. Factor the quadratic equation for m: $(m - 5)(m + 3) = 0$
  5. Determine the possible values for m: $m - 5 = 0$ or $m + 3 = 0$
  6. Therefore, the values are: $m = 5$ or $m = -3$.

Conclusion

The values of m for which the equation $(4 + m)x^2 + (m + 1)x + 1 = 0$ has equal roots are $5$ and $-3$.

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Important Questions from Quadratic Equation

  1. If 2x 2+ 5x + 1 = 0, then one of the values of \(x - \frac{1}{{2x}}\)  is:

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  3. If x 2 – 3x + 1 = 0, then the value of  \(\frac{(x^4+\frac{1}{x^2})}{(x^2+5x+1)}\)  is:

  4. If \(\sqrt{x}{}-{1\over\sqrt{x}}=\sqrt5\) \(x \ne 0\) , then what is the value of  \((x^4+{1\over{x^2}})\over(x^2+1) \)  ?

  5. If x 2\(\frac{1}{x^2}\)  = 18, x > 0, then find the value of x \(\frac{1}{x^3}\) .

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