The number of solutions for z3 + z = 0 ,

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 Multiple Choice QuestionsMultiple Choice Questions

251.

1 +i20111 - i2009 = ?

  • - 1

  • 1

  • 2

  • - 2


252.

In PQR,  R = π4, tanP3, tanQ3 are the roots of the equation ax2 + bx + c = 0, then

  • a +b = c

  • b + c = 0

  • a + c = 0

  • b = c


253.

The product of real of the equation x65 - 26x35 - 27 = 0

  • - 310

  • - 312

  • - 312/5

  • - 312/5


254.

If α, β, γ are the roots of the equation x3 + px2 + qx + r = 0, then the coefficient of x in the cubic equation whose roots are αβ + γ, βγ + α and γα + β is 

  • 2q

  • q2 + pr

  • p2 - qr

  • r(pq - r)


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255.

If z is complex number such that z - 4z = 2, then the greatest value of z is

  • 1 + 2

  • 2

  • 3 + 1

  • 1 + 5


256.

If α is a  non-real root of the equation x6 - 1 = 0,then α2 + α3  + α4 + α5α + 1 = ?

  • α

  • 1

  • 0

  • - 1


257.

If α and β are the roots of the equation x2 - 2x + 4 = 0, then α9 + β9 is equal to

  • - 28

  • 29

  • - 210

  • 210


258.

If a complex number z satisfied z2 - 1 = z2 + 1, then z lies on

  • the real axis

  • the imaginary axis

  • y = x

  • a circle


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259.

The number of solutions for z3 + z = 0 , is

  • 5

  • 1

  • 3

  • 2


A.

5

Given,  z3 + z = 0Let z = x + iy x + iy3 + x - iy = 0 x3 + iy3 + 3x2iy + 3xiy2 + x - iy = 0 x3 - y3i + 3x2yi - 3xy2 x - iy = 0 x2 - 3xy2 + x - y3 + 3x2y - yi = 0On equating real and imaginary parts, we getx3 - 3xy2 +x = 0or - y3 + 3x2y - y = 0 xx2 - 3y2 + 1 = 0or - yy2 - 3x2 + 1 = 0 x = 0 and y2 - 3x2 +1 = 0Now, x3 - 3y2 +1 = y2 - 3x2 +1, x3 - 3y2 + 1 = y2 - 3x2 + 1 4x2 = 4y2 x = ± yy2 - 3y2 + 1 = 0 2y2 = 1  y = ± 12 x = ± 12

Hence, their solutions are (0, 0) and (± 1/2, ± 1/2)

Hence, number of solutions is 5


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260.

If x = p + q, y =  + 2 and z = 2 + , where is a complex cube root of unity, then xyz equals to

  • p3 + q3

  • p3 - pq + q3

  • 1 + p3 + q3

  • p3 - q3


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