PUC Karnataka Science Class 12Department of Pre-University Education, Karnataka
Share

# Two Sides of a Triangle Have Lengths 'A' and 'B' and the Angle Between Them is θ What Value of θ Will Maximize the Area of the Triangle? Find the Maximum Area of the Triangle Also. - PUC Karnataka Science Class 12 - Mathematics

#### Question

Two sides of a triangle have lengths 'a' and 'b' and the angle between them is $\theta$. What value of $\theta$ will maximize the area of the triangle? Find the maximum area of the triangle also.

#### Solution

$\text { As, the area of the triangle, A } = \frac{1}{2}ab\sin\theta$

$\Rightarrow A\left( \theta \right) = \frac{1}{2}ab\sin\theta$

$\Rightarrow A'\left( \theta \right) = \frac{1}{2}\text { ab }\cos\theta$

$\text { For maxima or minima, A}'\left( \theta \right) = 0$

$\Rightarrow \frac{1}{2}ab\cos\theta = 0$

$\Rightarrow \cos\theta = 0$

$\Rightarrow \theta = \frac{\pi}{2}$

$\text { Also, A }''\left( \theta \right) = - \frac{1}{2}ab\sin\theta$

$\text { or,} A''\left( \frac{\pi}{2} \right) = - \frac{1}{2}ab\sin\frac{\pi}{2} = - \frac{1}{2}ab < 0$

$\text { i . e } . \theta = \frac{\pi}{2} \text { is point of maxima }$

$\text { Now },$

$\text { The maximum area of the triangle } = \frac{1}{2}ab\sin\frac{\pi}{2} = \frac{ab}{2}$

Is there an error in this question or solution?

#### Video TutorialsVIEW ALL [1]

Solution Two Sides of a Triangle Have Lengths 'A' and 'B' and the Angle Between Them is θ What Value of θ Will Maximize the Area of the Triangle? Find the Maximum Area of the Triangle Also. Concept: Graph of Maxima and Minima.
S