Optionals IAS Mains Mathematics: Questions 278 - 283 of 283

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Question 278

Appeared in Year: 2006

Describe in Detail


Solve: (Paper 2)


  • Given differential equation is

  • Hence auxiliary Equation is

    … eq. (1)

  • From last two members, we have

  • Integrating, we get

    … eq. (2)

  • From first and last members if (1) , we have

  • Putting

    We get

  • Which is ordinary differential equation of order 1

  • Hence general solution of given differential equation is

… (2 more words) …

Question 279

Appeared in Year: 2009

Describe in Detail


Show that where (Paper 1)







Adding vertically, we get

Question 280

Appeared in Year: 2007

Describe in Detail


Show that the planes cuts the cone in perpendicular lines. (Paper 1)


The equation of cone is

… eq. (1)

The equation of plane is

… eq. (2)

Comparing (1) with

We get


Necessary and sufficient condition that the cone may have three mutually perpendicular generators

The cone has three mutually perpendicular generators

The plane (2) cuts the cone (1) in perpendicular lines if the normal to the plane (2) through the v…

… (21 more words) …

Question 281

Appeared in Year: 2010

Describe in Detail


Let . Show that C is a commutative ring with 1 under point wise addition and multiplication. Determine whether C is an integral domain. Explain. (Paper 2)


  • Given

    Now is always continuous

  • Clearly, if given by

  • I. is Abelian group

    (i) let

    are real valued continuous function


  • We know that sum of two continuous function is continuous

    is also continuous

  • And sum of real valued function is real valued

    is also real valued

    is closed under addition.

  • (ii) let,


    is associative under addition

  • (iii) Existence o…

… (153 more words) …

Question 282

Describe in Detail


Let C be the field of complex numbers and let n be a positive integer . Let V be the vector space of all matrices over C. Which of the following sets of matrices A in V are subspaces of V?

1. All invertible A;

2. All non-invertible A;

3. All A such that , where B is some fixed matrix in V.


The answer to c is not correct, I guess.

H is a subspace of V if

  • The zero vector is an element of H
  • H is closed under addition: if a, b in H, then in H
  • H is closed under scalar multiplication: if in H and c a scalar then cx in H

is a subspace, because

  • 0, the zero matrix is in H, because
  • H is closed under addition: Let A, C in H, thus and , then, thu…

… (17 more words) …

Question 283


Describe in Detail


Prove that the union of two subspaces is a subspace if and only if one is contained in the other.


Let X and Y be two given subspace.

Case 1- one subspace is contained in other

X is contained in Y. then union X and Y will be Y. and since Y is already subspace, union will be subspace too.

Case 2- union is subspace.

  • Now assume X is not contained in Y. that is x does not lie in Y.
  • Let x belongs to X and y belongs to Y.
  • Subspace satisfies closure property…

… (57 more words) …