The function f(x) = x - 2 + x is from

Subject

Mathematics

Class

JEE Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

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11.

The function f(x) = x - 2 +x is

  • differentiable at both x = 2 and x = 0

  • differentiable at x = 2 but not at x = 0

  • continuous at x = 2 but not at x = 0

  • continuous at both x = 2and x = 0


D.

continuous at both x = 2and x = 0

fx = x - 2 + xFirst we check the continuityAt x = 0,RHL, f0 +h = limh00 + h - 2 + 0 - h                       = - 2 = 2LHL, f0 - h = limh00 - h - 2 + 0 - h                      = - 2 = 2At x = 2,RHL, f2 + h = limh02 + h - 2 + 2 + h                       = 0 + 2 + 0 = 2LHL, f2 + h = limh02 - h - 2 + 2 + h                      = 0 + 2 - 0 = 2

Hence, f(x), is continuous at x = 0, 2

Now, we check differentiability

         fx = - x +2 - x, x <0- x +2 - x, 0  x 2x -2 + 2, 2  x         fx = 2 - 2x, x <00, 0  x 22x - 2, 2  xNow, f'x = - 2, x <00, 0  x 22, 2  x

Hence, f(x) is not differentiable at x = 0, 2.


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12.

A wire of length 20 cm is bent in the form of a sector of a circle. The maximum area that can be enclosed by the wire is

  • 20 sq cm

  • 25 sq cm

  • 10 sq cm

  • 30 sq cm


13.

The condition for the line y = mx + c to be a normal to the parabola y2 = 4ax is

  • c = - 2am - am3

  • c = - am

  • c = am

  • c = 2am + am3


14.

If y = tan-1x2 - 1, then the ratio d2ydx2 : dydx is

  • xx2 - 11 - 2x2

  • 1 - 2x2xx2 - 1

  • 1 + 2x2xx2 + 1

  • xx2 + 11 - 2x2


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15.

P is the point of contact of the tangent form the origin to the curve y = loge(x). The length of the perpendicular drawn form the origin to the normal at P is

  • 12e

  • 1e

  • 2e2 + 1

  • e2 +1


16.

For the curve 4x5 = 5y4, the ratio of the cube of the subtangent at a point on the curve the square of the subnormal at the same point is

  • 445

  • 544

  • 4454

  • 544


17.

The set of real values of x for which f(x) = xlogx is increasing is

  • x :x  e

  • empty

  • {x : x < e}

  • {1}


18.

If a, b and c are non-zero coplanar vectors, then 2a - b 3b - c 4c - a is

  • 25

  • 0

  • 27

  • 9


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19.

A space vector makes the angles 150° and 60° with the positive direction of x-and y-axes. The angle made by the vector with the positive direction z-axis is

  • 90°

  • 60°

  • 180°

  • 120°


20.

If a, b and c are unit vectors, such that a + b + c = 0, then 3a . b + b . c + c . a= 0 is

  • - 1

  • 1

  • - 3

  • 3


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