WBBSEClass XMathematicsVariation03 Mark2024 Hard

QQuestion

If \frac{x}{y+z} = \frac{y}{z+x} = \frac{z}{ x+y}, then show that each ratio is \frac{1}{ 2} or -1.

Exam-ready answer 03 Mark

Answer

\frac{x}{y+z} = \frac{y}{z+x} = \frac{z}{x+y} = k (say)

⇒ x = k(y+z) — (i)

⇒ y = k(z+x) — (ii)

⇒ z = k(x+y) — (ii)

(i) + (ii) + (iii)

x + y + z = k(y+z) + k(z+x) + k(x+y)

or, x + y + z = k(y + z + z + x + x + y)

or, x + y + z = 2k(x + y + z)

or, (x + y + z) – 2k(x + y + z) = 0

or, (x + y + z) (1 – 2k) = 0

either, x + y + z = 0 or, 1 – 2k = 0 ⇒ k = \frac{1}{2}

Again,

x + y + z = 0

⇒ y + z = – x

\frac{x}{y + z} = -1

x + y + z = 0

⇒ x + z = – y

\frac{y}{x + z} = -1

x + y + z = 0

⇒ x + y = – z

\frac{z}{x + y} = -1

\frac{x}{y + z} = \frac{y}{x + z}\frac{z}{x + y} = -1 or \frac{1}{2} (Proved)

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