If the coefficients of x3 and x4 in the expansion of (1+ax+bx2)(

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81.
Let α and  β be the roots of equations x2-6x-2 = 0. If ann- βn, for n≥1, the value of a10-2a8/2a9 is equal to 
  • 6

  • -6

  • 3

  • 3

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82.

The normal to the curve x2 + 2xy-3y2 =0 at (1,1)

  • does not meet the curve again

  • meets the curve again in the second quadrant

  • meets the curve again in the third quadrant

  • meets the curve again in the third quadrant

247 Views

83.

If z is a complex number such that |z|≥2, then the minimum value of open vertical bar straight z space plus space 1 half close vertical bar

  • is equal to 5/2

  • lies in the interval (1,2)

  • is strictly greater than 5/2

  • is strictly greater than 5/2

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84.

Let α and β be the roots of equation px2 +qx r =0 p ≠0. If p,q and r are in AP and 1 over straight alpha space plus space 1 over straight beta = 4, then the value of |α- β| is

  • fraction numerator square root of 61 over denominator 9 end fraction
  • fraction numerator 2 square root of 17 over denominator 9 end fraction
  • fraction numerator square root of 34 over denominator 9 end fraction
  • fraction numerator square root of 34 over denominator 9 end fraction
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85.

If the coefficients of x3 and x4 in the expansion of (1+ax+bx2)(1-2x)18 in powers of x are both zero, then (a,b) is equal to

  • open parentheses 16 comma 251 over 3 close parentheses
  • open parentheses 14 comma 251 over 3 close parentheses
  • open parentheses 14 comma 272 over 3 close parentheses
  • open parentheses 14 comma 272 over 3 close parentheses


D.

open parentheses 14 comma 272 over 3 close parentheses

In expansion of (1+ax+bx2)(1-2x)18,
Coefficient of x3 = Coefficient of x3 in (1-2x)18
+Coefficient of x2 in a(1-2x)18
+Coefficient of x in b(1-2x)18
 = - negative straight C presuperscript 18 subscript 3.2 cubed space plus space straight a straight C presuperscript 18 subscript 2.2 squared minus straight b to the power of 18 straight C subscript 1.2 space equals space 0
rightwards double arrow fraction numerator 18 space straight x 17 space straight x space 16 over denominator 3 space straight x 2 end fraction.8 space plus space straight a. fraction numerator 18 space straight x 17 over denominator 2 end fraction 2 squared minus straight b.18.2 space equals 0
rightwards double arrow space 17 straight a minus straight b space equals space fraction numerator 34 space straight x space 16 over denominator 3 end fraction space space... space left parenthesis straight i right parenthesis
Similarly space coefficient space of space straight x to the power of 4
straight C presuperscript 18 subscript 4.2 to the power of 4 space plus space straight a straight C presuperscript 18 subscript 3.2 cubed minus straight b to the power of 18 straight C subscript 2.2 squared space equals space 0
therefore space 32 straight a minus 3 straight b equals space 240
On space solving space Eqs. space left parenthesis straight i right parenthesis space and space left parenthesis ii right parenthesis space we space get
straight a space equals space 16 space straight b space equals space 272 over 3

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86.

If [a x b b x c c x a] = λ[a b c]2, then λ is equal to 

  • 0

  • 1

  • 2

  • 2

261 Views

87.

The real number k for which the equation, 2x3 +3x +k = 0 has two distinct real roots in [0,1]

  • lies between 1 and 2

  • lies between 2 and 3

  • lies between -1 and 0

  • lies between -1 and 0

183 Views

88.

If the equations x2 + 2x + 3 = 0 and ax2 + bx + c = 0, a, b, c ∈ R, have a common root, then a : b : c is

  • 1:2:3

  • 3:2:1

  • 1:3:2

  • 1:3:2

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89.

If z is a complex number of unit modulus and argument θ, then arg open parentheses fraction numerator 1 plus straight z over denominator 1 plus straight z with bar on top end fraction close parentheses is equal to

  • π/2-θ

  • θ

  • θ

223 Views

90.

The equation esinx-e-sinx -4 = 0 has

  • infinite number of real roots

  • No real root

  • exactly one real root

  • exactly one real root

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