A tower subtends angles α, 2α and 

Subject

Mathematics

Class

JEE Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

If in ABC, r1 < r2 < r3, then :

  • a < b < c

  • a > b > c

  • b > a < c

  • a < c < b


2.

In a ABC, if 3a = b + c, then cotB2cotC2 is equal to :

  • 1

  • 2

  • 3

  • 4


3.

If in a triangle, if b = 20, c = 21 and sinA = 35, then a is equal to

  • 12

  • 13

  • 14

  • 15


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4.

A tower subtends angles α, 2α and 3α respectively at points A, B and C, all lying on a horizontal line through the foot of the tower,then ABBC is equal to :

  • sin3αsin2α

  • 1 + 2cos2α

  • 2cos2α

  • sin2αsinα


B.

1 + 2cos2α

In ECD,    tan3α = hCD

 CD = hcot3α      ...iIn EBD,tan2α = hBD  BD = hcot2α     ...iiIn EAD,  tanα = hAD  AD = hcotα        ...iiiFrom Eqs. (ii) and (iii),AD- BD = hcotα - hcot2α          AB = hcotα - cot2α     ...iv

From Eqs. (i) and (ii), we getBD - CD = hcot2α - hcot3α          BC = hcot2α - cot3α        ...vFrom Eqs. (iv) and (v), we get     ABBC = hcotα - cot2α2cot2α - cot3α ABBC = cosαsinα - cos2αsin2αcos2αsin2α - cos3αsin3α = sin2α - αsinαsin2αsin3α - 2αsin2αsin3α            = sin3αsinα = 3sinα - 4sin3αsinα           = 3 - 4sin2α

         = - 3 - 21 - cos2α= 1 + 2cos2α


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5.

A bag X contains 2 white and 3 black balls and another bag Y contains 4 white and 2 black balls. One bag is selected at random and a ballis drawn from it. Then, the probability for the ball chosen be white, is :

  • 215

  • 715

  • 815

  • 1415


6.

For a poisson variate X, if P(X = 2) = 3P(X = 3), then the mean of X is :

  • 1

  • 12

  • 13

  • 14


7.

A random variate X takes the values 0, 1, 2, 3 and its mean is 1.3. If P(X = 3) = 2P(X = 1) and P(X = 2) = 0.3, then P(X = 0) is equal to :

  • 0.1

  • 0.2

  • 0.3

  • 0.4


8.

The co-ordinate axes are rotated through an angle 135°. If the co-ordinates of a point P inthe new system are known to be (4, - 3), then the co-ordinates of P in the original system are :

  • 12, 72

  • 12, - 72

  • - 12, - 72

  • - 12, 72


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9.

The point P is equidistant from A(1, 3), B(- 3, 5)and C(5, - 1), then PA is equal to

  • 5

  • 55

  • 25

  • 510


10.

If the lines 4x + 3y - 1 = 0, x - y + 5 = 0 and kx + 5y - 3 are concurrent, then k is equal to

  • 4

  • 5

  • 6

  • 7


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