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If area of DeltaABC (Delta) and angle C ...

If area of `DeltaABC (Delta)` and angle C are given and if c opposite to given angle is minimum, then

A

`a = sqrt((2Delta)/(sinC))`

B

`b = sqrt((2Delta)/(sinC))`

C

`a = (4Delta)/(sinC)`

D

`b = (4Delta)/(sin^(2)C)`

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The correct Answer is:
To solve the problem, we need to find the condition under which the side \( c \) opposite to angle \( C \) is minimized, given the area \( \Delta \) of triangle \( ABC \) and angle \( C \). ### Step-by-Step Solution: 1. **Understanding the relationship between area, sides, and angles**: The area \( \Delta \) of triangle \( ABC \) can be expressed using the formula: \[ \Delta = \frac{1}{2}ab \sin C \] where \( a \) and \( b \) are the lengths of the sides adjacent to angle \( C \). 2. **Rearranging the area formula**: From the area formula, we can express \( ab \) in terms of \( \Delta \) and \( \sin C \): \[ ab = \frac{2\Delta}{\sin C} \] 3. **Using the Law of Cosines**: According to the Law of Cosines, we have: \[ c^2 = a^2 + b^2 - 2ab \cos C \] 4. **Substituting \( ab \) into the Law of Cosines**: We can substitute \( ab = \frac{2\Delta}{\sin C} \) into the equation for \( c^2 \): \[ c^2 = a^2 + b^2 - 2 \left(\frac{2\Delta}{\sin C}\right) \cos C \] 5. **Minimizing \( c \)**: To minimize \( c \), we need to minimize \( c^2 \). We can analyze the expression: \[ c^2 = a^2 + b^2 - \frac{4\Delta \cos C}{\sin C} \] To minimize \( c^2 \), we can use the condition that \( a \) and \( b \) should be equal (i.e., \( a = b \)). This is because, for a fixed area and angle, the triangle is most compact (and thus has the smallest \( c \)) when it is isosceles. 6. **Setting \( a = b \)**: Let \( a = b \). Then we can denote \( a \) as \( A \): \[ c^2 = 2A^2 - \frac{4\Delta \cos C}{\sin C} \] 7. **Finding the value of \( A \)**: Using the area formula again: \[ \Delta = \frac{1}{2}A^2 \sin C \] Rearranging gives: \[ A^2 = \frac{2\Delta}{\sin C} \] 8. **Final expression for \( c^2 \)**: Substituting \( A^2 \) back into the expression for \( c^2 \): \[ c^2 = 2 \left(\frac{2\Delta}{\sin C}\right) - \frac{4\Delta \cos C}{\sin C} \] Simplifying this gives: \[ c^2 = \frac{4\Delta}{\sin C} (1 - \cos C) \] ### Conclusion: Thus, the minimum value of \( c \) occurs when \( a = b \) and is given by: \[ c = \sqrt{\frac{4\Delta}{\sin C} (1 - \cos C)} \]

To solve the problem, we need to find the condition under which the side \( c \) opposite to angle \( C \) is minimized, given the area \( \Delta \) of triangle \( ABC \) and angle \( C \). ### Step-by-Step Solution: 1. **Understanding the relationship between area, sides, and angles**: The area \( \Delta \) of triangle \( ABC \) can be expressed using the formula: \[ \Delta = \frac{1}{2}ab \sin C ...
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CENGAGE ENGLISH-PROPERTIES AND SOLUTIONS OF TRIANGLE-Multiple correct answer type
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