A) 2m
B) 4m
C) 1m
D) 3m
Correct Answer: D
Solution :
Let A be the area, b be the breadth and \[\ell \] be the length of the rectangle. Given: \[\frac{dA}{dt}=-5,\frac{d\ell }{dt}=2m,\frac{db}{dt}=-3\] We know,\[A=\ell \times b\] \[\Rightarrow \]\[\frac{dA}{dt}=\ell .\frac{db}{dt}+b.\frac{d\ell }{dt}=-3\ell +2b\] \[\Rightarrow \]\[-5=-3\ell +2b.\]When b = 2, we have \[-5=-3\ell +4\Rightarrow \ell =\frac{9}{3}=3m\]You need to login to perform this action.
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