1.

Side of an equilateral triangle expands at therate of 2 cm/sec. The rate of increase of its area when each side is 10 cm is(a)cm2/sec (b)cm2/sec(c) 10 cm2/sec (d) 5 cm2/secA. `10sqrt(2)cm^(2)//sec`B. `10sqrt(3)cm^(2)//sec`C. `10 cm^(2)//sec`D. `5cm^(2)//sec`

Answer» Correct Answer - B
Let x be the side and A be the area of equilateral triangle at time t. Then,
`A=(sqrt(3))/(4)x^(2)`
`implies(dA)/(dt)=sqrt(3)/(2)xx(dx)/(dt)`
`implies(dA)/(dt)=(sqrt(3))/(2)xx10xx2=10sqrt(3)" "[because x=10 and (dx)/(dt)=2]`


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