Let l be the length and b be the breadth of a rectangle such that

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 Multiple Choice QuestionsMultiple Choice Questions

21.

What is the minimum value of a2cos2x + b2sin2x, where a > 0 and b > 0 ?

  • (a + b)2

  • (a - b)2

  • a2  + b2

  • a2 + b2


22.

If fx = x23 - 5x22 + 6x + 7 increases in the interval T and decreases in the interval S, then which one of the following is correct ?

  • T = - , 2  3,  and S = 2, 3

  • T = φ and S =  - , 

  • T =  - ,  and S = φ

  • T = 2, 3 and S = - , 2  3, 


23.

Consider the function

f(x) = 3x4 – 20x3 – 12x2 + 288x + 1

In which one of the following intervals is the function decreasing ?

  • ( - 2, 3)

  • (3, 4)

  • (4, 6)

  • No


24.

Consider the function

f(x) = 3x4 – 20x3 – 12x2 + 288x + 1

In which one of the following intervals is the function increasing ?

  • ( - 2, 3)

  • (3, 4)

  • (4, 6)

  • (6, 9)


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25.

Let l be the length and b be the breadth of a rectangle such that l x b = k. What is the maximum area of the rectangle ?

  • 2k2

  • k2

  • k22

  • k24


D.

k24

Here ABCD is rectangle which have

Length AB = l and breadth BC = b

Let area is y

l + b = k

l = k - b  (given)

Now, area y = lb = l(k - l) = kl - l2

For maximum area y,

     dydl = 0   ...ik - 2l = 0         l = k2When differentiating eqn (i) dy2dl2 = - 2 < 0Hence y has maximum value when l = k2 b = k2 maximum area k2 . k2 = k24


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26.

What is the minimum value of 3cosA + π3 where A ∈ R ?

  • - 3

  • - 1

  • 0

  • 3


27.

The radius of a circle is increasing at the rate of 0.7 cm/sec. What is the rate of increase of its circumference ?

  • 4.4 cm/sec

     

  • 8.4 cm/sec

  • 8.8 cm/sec

  • 15.4 cm/sec


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