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Two observers are stationed due north of a tower (of height x metre) at a distance y metre from each other. The angles of elevation of the tower observed by them are 30° and 45° respectively. Then xyfrac{x}{y} is equal to

a

312frac{sqrt{3}-1}{2}

b

1

c

212frac{sqrt{2}-1}{2}

d

3+12frac{sqrt{3}+1}{2}

Answer : Option D
Explanation :

PSQ=45,PRQ=30angle mathrm{PSQ}=45^{circ}, angle mathrm{PRQ}=30^{circ}

From ΔPQS

tan45=PQQS an 45^{circ}=frac{mathrm{PQ}}{mathrm{QS}}

1=xQSQS=xRightarrow 1=frac{x}{mathrm{QS}} Rightarrow mathrm{QS}=x metre

From ΔPQR,

tan30=PQQR an 30^{circ}=frac{mathrm{PQ}}{mathrm{QR}}

13=xx+yRightarrow frac{1}{sqrt{3}}=frac{x}{x+y}

3x=x+yRightarrow sqrt{3} x=x+y

3xx=yRightarrow sqrt{3} x-x=y

x(31)=yRightarrow x(sqrt{3}-1)=y

xy=131=3+1(31)(3+1)Rightarrow frac{x}{y}=frac{1}{sqrt{3}-1}=frac{sqrt{3}+1}{(sqrt{3}-1)(sqrt{3}+1)}

=3+131=3+12=frac{sqrt{3}+1}{3-1}=frac{sqrt{3}+1}{2} metre

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