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maliyeci
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if one of the roots of the equation \(x^2+4x-7=0\) is \(a\), then what is the result of the multiplication below?
\((a-1).(a+1).(a+3).(a+5)=?\)

a)12 b)14 c)15 d)18 e)20[/quote]

rephrase question: (a-1).(a+5).(a+3).(a+1) =(a^2+4a+3)(a^2+4a-5)

from stem

a^2+4a = 7

thus subst:
(7+3)(7-5) = 20...E
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Good solution yezz +1 ;)
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Good solution yezz +1 ;)

excellent GMAT-type question.. thanks for sharing.
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maliyeci
Another question:

What is the equal of \(sqrt{5-sqrt{21}}\)
Answer is

Does not anybody have any solution to this problem???
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maliyeci
Another question:

What is the equal of \(sqrt{5-sqrt{21}}\)
Answer is

Does not anybody have any solution to this problem???

we can brute force it but i am sure there is an eithier way...that i dont know of :)
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\(sqrt{5-sqrt{21}}\)???

\(5-sqrt{21} = \\
1/2*(10-2*sqrt{21})=\\
1/2*(7+3-2*sqrt{21})=\\
1/2*(sqrt{7}-sqrt{3})^2\)
Thus
\(sqrt{5-sqrt{21}}\)=

\(sqrt{1/2*(sqrt{7}-sqrt{3})^2}=\\
(sqrt{7}-sqrt{3})/sqrt{2}\)
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\(sqrt{5-sqrt{21}}\)???

\(5-sqrt{21} = \\
1/2*(10-2*sqrt{21})=\\
1/2*(7+3-2*sqrt{21})=\\
1/2*(sqrt{7}-sqrt{3})^2\)
Thus
\(sqrt{5-sqrt{21}}\)=

\(sqrt{1/2*(sqrt{7}-sqrt{3})^2}=\\
(sqrt{7}-sqrt{3})/sqrt{2}\)


to be honest , it wouldnt have even crossed my mind in a million light years .:) ...great sol, Kudos+1 from me
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This forum showed me a lot of this type good solutions. Thanks for all.
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An easy one:
a and b are positive numbers.
LCM(a,b)=\(2.3^2\)
How many different (a,b) numbers are there?
a)6
b)12
c)13
d)14
e)15
Note:(a,b) is different from (b,a)

Answer is


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