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Question

Consider the following for the next items that follow:

Let \(\rm \frac{(x-a)(x-b)}{(x-m a)(x-m b)}=\frac{(x+a)(x+b)}{(x+m a)(x+m b)}\); m, a, b > 0.

What is x equal to ?

This question was previously asked in
CDS I 2023 English Previous Year Paper (16-April-2023)
The correct answer is \(\pm \sqrt{\mathrm{mab}}\)

Concept:

Componendo Dividendo Rule:

If (a + b ) : (a – b) = (c + d) : (c – d), than

a : b = c : d

Calculation:

According to the question,

\(\rm \frac{(x-a)(x-b)}{(x-m a)(x-m b)}=\frac{(x+a)(x+b)}{(x+m a)(x+m b)}\)

⇒ \((x - a) (x - b) \over (x + a) (x + b) \) = \((x - ma) (x - mb) \over (x + ma) (x + mb)\)

⇒ \(x^2 - (a + b)x + ab \over x^2 + (a + b)x + ab\) = \(x^2 - (ma + mb)x + m^2ab \over x^2 + (ma + mb)x + m^2ab \)

By componendo dividendo method,

⇒ \(x^2 + ab \over (a + b)x \) = \(x^2 + m^2 ab \over (ma + mb)x \)

⇒ \(x^2 + ab \over x^2 + m^2 ab\) = \((a + b) \over (a + b) m\)

⇒ \(x^2 + ab \over x^2 + m^2 ab\) = \(1 \over m\)

⇒ mx2 + mab = x2 + m2ab

⇒ mx2 - x2 = m2ab - mab

⇒ x2 (m - 1) = mab (m - 1)

⇒ x2 = mab

⇒ x = \(\pm \sqrt{\mathrm{mab}}\)

∴ The value of x is equal to \(\pm \sqrt{\mathrm{mab}}\).

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Similar Questions

  1. What is \(\rm \frac{x^2+a b}{x^2+m^2 a b}\) equal to? 

  2. If \({\rm{x}} = \frac{{\sqrt {{\rm{a}} + {\rm{b\;}}} -{\rm{\;}}\sqrt {{\rm{a}} - {\rm{b}}} }}{{\sqrt {{\rm{a}} + {\rm{b}}} {\rm{\;}} + {\rm{\;}}\sqrt {{\rm{a}} - {\rm{b\;}}} }}\) , then what is bx 2– 2ax + b equal to (b ≠ 0)?

  3. For \(x = \frac{{4\sqrt 6 }}{{\sqrt 2 + \sqrt 3 }},\)what is the value of \(\frac{{x + 2\sqrt 2 }}{{x - 2\sqrt 2 }} + \frac{{x\; + \;2\sqrt 3 }}{{x - 2\sqrt 3 }}?\)

  4. If \(\rm \frac{a+b}{b+c}=\frac{c+d}{d+a}\) a ≠ c, then which one of the following is correct ?

  5. If (3a + 6b + c + 2d) × (3a - 6b - c + 2d) = (3a - 6b + c - 2d) × (3a + 6b - c - 2d), then which one of the following is correct?

  6. Consider the following statements:

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Important Questions from Componendo or Dividendo

  1. If \(\frac{x}{y} = \frac{5}{3}\), then \(\frac{x + y}{x - y}\) is equal to

  2. What is \(\rm \frac{x^2+a b}{x^2+m^2 a b}\) equal to? 

  3. If \(\frac b a = 0.7,\)  find the value of  \(\frac {a-b}{a+b} + \frac {11}{34}.\)

  4. If \({\rm{x}} = \frac{{\sqrt {{\rm{a}} + {\rm{b\;}}} -{\rm{\;}}\sqrt {{\rm{a}} - {\rm{b}}} }}{{\sqrt {{\rm{a}} + {\rm{b}}} {\rm{\;}} + {\rm{\;}}\sqrt {{\rm{a}} - {\rm{b\;}}} }}\) , then what is bx 2– 2ax + b equal to (b ≠ 0)?

  5. For \(x = \frac{{4\sqrt 6 }}{{\sqrt 2 + \sqrt 3 }},\)what is the value of \(\frac{{x + 2\sqrt 2 }}{{x - 2\sqrt 2 }} + \frac{{x\; + \;2\sqrt 3 }}{{x - 2\sqrt 3 }}?\)

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