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Thursday, June 14, 2012

Application of the Cayley-Hamilton Theorem

Cayley-Hamilton Theorem, a basic theorem from Linear Algebra, is not a part of JEE syllabus. But this simple result comes in handy in JEE often.

According to the Cayley-Hamilton Theorem, every square matrix A satisfies its own Characteristic Equation.

For a matrix A of size n X n, the Characteristic Equation in variable is defined as,
,
where I is the identity matrix of size n X n.
So according to the Cayley-Hamilton Theorem, we have,




This can be illustrated with an example.

Consider,
Then,

From the Cayley-Hamilton Theorem,

And it can be verified that the above result is indeed correct.

Problem 1
Let

Suppose
Then determine c and d.
                                                                                                 (IIT-JEE 2005)
 Solution 1
 The given equation gives,


By applying the Cayley-Hamilton Theorem on A, we have,



Direct comparison of (1) and (2) gives c=-6 and d=11

2 comments:

  1. thnsk for the application i ask this in my Iit jee coaching classes few days back

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  2. given is unit vector n=(n1,n2,n3) and a real constant a. ue the cayley hamilton theorem to evaluate exp{ian. rho}
    here rho is pauli matrices and n. rho=n1rho1+n2rho2+n3.rho3 and exponential of matrix is deifned by usual exponent

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