If P =  is the adjoint of a 3 x3 matrix A and |A| = 4, then �

Subject

Mathematics

Class

JEE Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

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21.

If P = open square brackets table row 1 straight alpha 3 row 1 3 3 row 2 4 4 end table close square brackets is the adjoint of a 3 x3 matrix A and |A| = 4, then α is equal to 

  • 4

  • 11

  • 5

  • 5


B.

11

Given, 
straight P space equals space open square brackets table row 1 straight alpha 3 row 1 3 3 row 2 4 4 end table close square brackets
|P| = 1(12-12)-α (4-6) +3(4-6)
 = 2α -6.
∵ P =adj(A)
∴ |P| = |adj A | = |A|3-1 = |A|2 = 16
[∵ |adj A| = |A|n-1 order is 3 x3
∴ 2α -6 = 16
2α = 22
α = 11

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22.

If y  = sec (tan-1 x), then dy/dx at x = 1 is equal to 

  • fraction numerator 1 over denominator square root of 2 end fraction
  • 1 half
  • 1

  • 1

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23.

Distance between two parallel planes 2x + y + 2z = 8 and 4x + 2y + 4z + 5 = 0 is

  • 3/2

  • 5/2

  • 7/2

  • 7/2

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24.

At present, a firm is manufacturing 2000 items. It is estimated that the rate of change of production P with respect to the additional number of workers x is given by dP over dx space equals space 100 minus 12 square root of straight x. If the firm employs 25 more workers, then
the new level of production of items is

  • 2500

  • 3000

  • 3500

  • 3500

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25.

If the lines

fraction numerator straight x minus 2 over denominator 1 end fraction space equals space fraction numerator straight y minus 3 over denominator 1 end fraction space equals space fraction numerator straight z minus 4 over denominator negative straight k end fraction
and
fraction numerator straight x minus 1 over denominator straight k end fraction space equals space fraction numerator straight y minus 4 over denominator 2 end fraction space equals space fraction numerator straight z minus 5 over denominator 1 end fraction
are coplanar, then k can have

  • any value

  • exactly one value

  • exactly two values

  • exactly two values

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26.

If the vectors AB = 3î + 4k̂ and AC = 5î - 2ĵ + 4k̂ are the sides of a Δ ABC, then the length of the median through A is 

  • √18

  • √72

  • √33

  • √45

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27.

If ∫f x dx =Ψ (x),then ∫x5 f(x3)dx is equal to

  • 1 third space open square brackets straight x cubed straight psi left parenthesis straight x cubed right parenthesis minus integral straight x squared space straight psi left parenthesis straight x cubed right parenthesis dx close square brackets space plus straight C
  • 1 third space straight x cubed straight psi left parenthesis straight x cubed right parenthesis minus 3 integral straight x squared space straight psi left parenthesis straight x cubed right parenthesis dx space plus straight C
  • 1 third straight x cubed straight psi left parenthesis straight x cubed right parenthesis minus integral straight x squared space straight psi left parenthesis straight x cubed right parenthesis dx space plus space straight C
  • 1 third straight x cubed straight psi left parenthesis straight x cubed right parenthesis minus integral straight x squared space straight psi left parenthesis straight x cubed right parenthesis dx space plus space straight C
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28.

Statement I - The value of the integral integral subscript straight pi divided by 6 end subscript superscript straight pi divided by 3 end superscript fraction numerator dx over denominator 1 plus space square root of tan space straight x end fraction is equal to π/6.
Statement II-integral subscript straight a superscript straight b straight f left parenthesis straight x right parenthesis space dx space equals space integral subscript straight a superscript straight b straight f left parenthesis straight a plus straight b minus straight x right parenthesis space dx

  • Statement -I is True; Statement -II is True; Statement-II is a correct explanation for Statement-I

  • Statement - I is True; Statement -II is true; Statement-II is not a correct explanation for Statement-I

  • Statement -I is True; Statement -II is False.

  • Statement -I is True; Statement -II is False.

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29.

The area (in square units) bounded by the curves y = straight y space equals space square root of straight x comma 2y-x+3 =0, X -axis and lying in the first quadrant is 

  • 9

  • 36

  • 18

  • 18

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30.

The intercepts on X- axis made by tangents to the curve, straight y space equals space integral subscript 0 superscript straight x vertical line straight t vertical line space dt comma space straight x space straight epsilon space straight R which are parallel to the line y =2x, are equal to

  • ±1

  • ±2

  • ±3

  • ±3

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