Question

A triangle has two constant sides of length 5 feet and 7 feet. The angle between these two sides is increasing at a rate of 0.9 radians per second. Find the rate at which the area of the triangle is changing when the angle between the two sides is ????5.

Answer 1

Answer:$12.74 ft^2/s$

Step-by-step explanation:

Given

Two sides of triangle of sides 5 ft and 7 ft

and angle between them is increasing at a rate of 0.9 radians per second

let $\theta$is the angle between them thus

Area of triangle when two sides and angle between them is given

$A=\frac{ab\sin C}{2}$

$A=\frac{5\times 7\times \sin \theta }{2}$

Differentiate w.r.t time

$\frac{\mathrm{d} A}{\mathrm{d} t}=\frac{35\cos theta }{2}\times \frac{\mathrm{d} \theta }{\mathrm{d} t}$

at $\theta =\frac{\pi }{5}$

$\frac{\mathrm{d} A}{\mathrm{d} t}=\frac{35\times cos(\frac{\pi }{5})}{2}\times 0.9$

$\frac{\mathrm{d} A}{\mathrm{d} t}=12.74 ft^2/s$