Answer:
(c) 1.6
Step-by-step explanation:
Given, xy = 20 and both x, y are functions of t.
So,
⇒ [tex]\frac{d(xy)}{dt} = x\frac{dy}{dt} + y\frac{dx}{dt}[/tex]
now, when x = 4, y will be 5 as xy = 20.
by subtituting the values in above equation, we get;
⇒ [tex]\frac{d(20)}{dt} = 4(-2) + 5\frac{dx}{dt}[/tex]
⇒ [tex]0 = -8 + 5\frac{dx}{dt}[/tex]
⇒ [tex]\frac{dx}{dt} = \frac{8}{5}[/tex]
⇒ [tex]\frac{dx}{dt} = 1.6[/tex]
