Power 4 Determinant!

If A A is a square matrix such that A = 1024 |A|=1024 and 1 4 A = 4 |\frac{1}{4}A|=4 , then what is adj A |\text{adj }A| ?

4 16 4^{16} 4 20 4^{20} 4 12 4^{12} 4 10 4^{10} 4 15 4^{15} 4 5 4^5 4 2

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2 solutions

Hem Shailabh Sahu
Apr 24, 2015

For a square matrix 'A' of order nxn or simply 'n' and a constant 'k', k A = ( k n ) A |kA|=(k^{n})|A| & a d j ( A ) = A n 1 |adj(A)|={|A|}^{n-1}

1 4 A = 4 |\frac{1}{4}A|=4 Therefore, 1 4 A = ( 1 4 ) n A = 4 |\frac{1}{4}A|=(\frac{1}{4})^{n}|A|=4 A = 1024 = 2 10 = 4 5 |A|=1024=2^{10}=4^5 1 4 n . 4 5 = 4 n = 4 \Rightarrow \frac{1}{4^n}.4^5=4 \Rightarrow n=4

Therefore, a d j ( A ) = A n 1 = ( 4 5 ) 4 1 = 4 3 5 = 4 15 |adj(A)|={|A|}^{n-1}=(4^5)^{4-1}=4^{3*5}=\boxed{4^{15}}

Gagan Raj
Apr 23, 2015

1 4 A = 4 |\frac{1}{4}A|=4

( 1 4 ) n (\frac{1}{4})^{n} A = 4 |A|=4

4 n 4^{-n} × \times 4 5 = 4 4^5=4

n + 5 = 1 -n+5=1

n = 4 n=4

So , a d j A = A n 1 = ( 4 5 ) 3 = 4 15 |adj~A|=|A|^{n-1}=(4^{5})^{3}=4^{15}

Hey @Gagan Raj How did you solve HYDRA ? Can you give me a hint to solve it?

Nihar Mahajan - 6 years, 1 month ago

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Well there are two HYDRA problems. One is by Sharky Kesa and the other one is by Daniel Ploch. Both the problems almost use the same method but which one do you want to solve ????? @Nihar Mahajan

Gagan Raj - 6 years, 1 month ago

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Click the "hydra" word in the comment above.And both the problems don't use the same method , they are different. I want help in Sharky's problem

Nihar Mahajan - 6 years, 1 month ago

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@Nihar Mahajan Well i dont think it is a good idea helping a fellow brilliant mate in the problems which he hasn't solved but this is all i can do for you.....use Probability......find the number of ways hydra's n n heads can be killed......summate all probabilities.....approximate the answer which is obtained in decimals and then use the following condition to get the final answer !!!!!

Gagan Raj - 6 years, 1 month ago

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@Gagan Raj I understood the solution . Sorry for the trouble.

Nihar Mahajan - 6 years, 1 month ago

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