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10^4 (5^4 – 2^4) / 21 =

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10^4 (5^4 – 2^4) / 21 =

by sanju09 » Fri Jun 18, 2010 4:23 am
10^4 (5^4 - 2^4) / 21 =
(A) 290,000
(B) 289,000
(C) 209,000
(D) 40,000
(E) 10,000
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by selango » Fri Jun 18, 2010 4:27 am
290,000

option A
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by kvcpk » Fri Jun 18, 2010 4:29 am
10^4 (5^4 - 2^4) / 21 = 10^4 * (5^2 + 2^2) * (5^2 - 2^2) / 21 = 10^4 * (5^2 + 2^2) = 29 * 10^4

Answer A
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by selango » Fri Jun 18, 2010 4:30 am
=10^4*[(5^2)^2-(2^2)^2]/21

=10^4[(5^2+2^2)(5^2-2^2)]/21

=10^4*29*21/21

=290000
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by amising6 » Fri Jun 18, 2010 4:30 am
10^4 (5^4 - 2^4) / 21 =

(5^4- 2^4)
=(25^2 -4^2)
=(25+4)(25-4) since a^2-b^2=(a+b)(a-b)
=(29)(21)


so this can be written as
(10^4 *29*21) / 21 = /21
=10^4*29
290,
hence option A000
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