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AL, BM and CN are perpendicular from ang...

AL, BM and CN are perpendicular from angular points of a triangle ABC on the opposite sides BC, CA and AB respectively. `Delta` is the area of triangle ABC, (r ) and R are the inradius and circumradius.
If perimeters of `DeltaLMN and Delta ABC an lamda and mu, ` then the value of `(lamda)/(mu)` is

A

`r/R`

B

`R/r`

C

`(rR)/(Delta)`

D

`(Delta)/(rR)`

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The correct Answer is:
To solve the problem, we need to find the ratio \(\frac{\lambda}{\mu}\), where \(\lambda\) is the perimeter of triangle \(LMN\) and \(\mu\) is the perimeter of triangle \(ABC\). ### Step-by-Step Solution: 1. **Understanding the Perimeters**: - The perimeter of triangle \(ABC\) is denoted as \(\mu\). - The perimeter of triangle \(LMN\) is denoted as \(\lambda\). 2. **Finding the Perimeter of Triangle \(ABC\)**: - The perimeter \(\mu\) of triangle \(ABC\) can be expressed as: \[ \mu = AB + BC + CA = a + b + c \] where \(a\), \(b\), and \(c\) are the lengths of the sides of triangle \(ABC\). 3. **Finding the Perimeter of Triangle \(LMN\)**: - The sides of triangle \(LMN\) can be expressed in terms of the angles and sides of triangle \(ABC\). The lengths of the sides of triangle \(LMN\) can be given by: \[ LM = BC \cdot \cos A, \quad MN = CA \cdot \cos B, \quad NL = AB \cdot \cos C \] - Thus, the perimeter \(\lambda\) can be expressed as: \[ \lambda = LM + MN + NL = (BC \cdot \cos A) + (CA \cdot \cos B) + (AB \cdot \cos C \] 4. **Using the Sine Rule**: - We can relate the sides of triangle \(ABC\) to its circumradius \(R\) and area \(\Delta\): \[ a = 2R \sin A, \quad b = 2R \sin B, \quad c = 2R \sin C \] 5. **Expressing \(\lambda\) in Terms of \(R\)**: - Substituting the expressions for \(a\), \(b\), and \(c\) into the perimeter of triangle \(LMN\): \[ \lambda = 2R(\sin A \cdot \cos A + \sin B \cdot \cos B + \sin C \cdot \cos C) \] - Using the identity \(\sin A \cos A = \frac{1}{2} \sin 2A\), we can rewrite \(\lambda\): \[ \lambda = R(\sin 2A + \sin 2B + \sin 2C) \] 6. **Finding the Ratio \(\frac{\lambda}{\mu}\)**: - We know that the perimeter \(\mu\) can also be expressed in terms of the semi-perimeter \(s\): \[ \mu = 2s = 2 \cdot \frac{a + b + c}{2} = a + b + c \] - Using the relationship between area \(\Delta\), inradius \(r\), and semi-perimeter \(s\): \[ \Delta = r \cdot s \] - Thus, we can express \(\mu\) in terms of \(r\): \[ \mu = 2s = \frac{2\Delta}{r} \] 7. **Final Ratio**: - Now we can find the ratio: \[ \frac{\lambda}{\mu} = \frac{R(\sin 2A + \sin 2B + \sin 2C)}{\frac{2\Delta}{r}} = \frac{R \cdot r}{\Delta} \] - After simplification, we find that: \[ \frac{\lambda}{\mu} = \frac{r}{R} \] ### Conclusion: The value of \(\frac{\lambda}{\mu}\) is \(\frac{r}{R}\).
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ARIHANT MATHS ENGLISH-PROPERTIES AND SOLUTION OF TRIANGLES -Exercise (Passage Based Questions)
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  2. Let ABC to be an acute triangle with BC=a,CA =b and AB=c, where a ne ...

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  3. Let ABC to be an acute triangle with BC=a,CA =b and AB=c, where a ne ...

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  4. Let ABC to be an acute triangle with BC=a,CA =b and AB=c, where a ne ...

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  5. In an acute angled triangle ABC, let AD, BE and CF be the perpendicula...

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  6. In an acute angle Delta ABC, let AD, BE and CF be the perpendicular fr...

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  7. In an acute angle Delta ABC, let AD, BE and CF be the perpendicular fr...

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  8. Let a,b, c are the sides opposite to angles A, B , C respectively in a...

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  9. Let a,b, c are the sides opposite to angles A, B , C respectively in a...

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  10. Let a,b, c are the sides opposite to angles A, B , C respectively in a...

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  11. When any two sides and one of the opposite acute angle are given, unde...

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  12. When any two sides and one of the opposite acute angle are given, unde...

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  13. When any two sides and one of the opposite acute angle are given, unde...

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  14. Consider a triangle ABC, where c,y,z are the length of perpendicular d...

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  15. Consider a triangle ABC, where c,y,z are the length of perpendicular d...

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  16. Consider a triangle ABC, where c,y,z are the length of perpendicular d...

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  17. AL, BM and CN are perpendicular from angular points of a triangle ABC ...

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  18. AL, BM and CN are perpendicular from angular points of a triangle ABC ...

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