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To the power 4

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by sakurle » Sat Sep 05, 2009 6:22 pm
If x^4 + y^4 = 100 greatest value of x is between

A. 0 and 3
B. 3 and 6
C. 6 and 9
D. 9 and 12
E. 12 and 15

The answer has to be either A or B, but which would you choose.
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by bharathh » Sat Sep 05, 2009 6:25 pm
A

For any of the other options x^4 would be > 100 and y^4 cannot be negative.
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by tom4lax » Sat Sep 05, 2009 6:33 pm
Actually i think the answer is B. 3^2=9, so x can be greater than 3, falling between 3 and 6.
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by bharathh » Sat Sep 05, 2009 6:43 pm
Hmm.. you could be right.

Dammit I was on a roll today :(

2 questions wrong then

Ok .. you def are correct
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by sakurle » Sun Sep 06, 2009 7:39 am
Yes the right answer is B between 3 to 6, but I am not sure how. Because if you take 4 4^4 is above 100.

However if you take x as 3.1, then x^4 = 92.351 which is still less than 100, and then y can taka a value such that y^4 added to x^4 can be 100. May be that is why the answer is B.
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Re: To the power 4

by tohellandback » Sun Sep 06, 2009 10:11 pm
sakurle wrote:If x^4 + y^4 = 100 greatest value of x is between

A. 0 and 3
B. 3 and 6
C. 6 and 9
D. 9 and 12
E. 12 and 15

The answer has to be either A or B, but which would you choose.
IMO B
to maximize x^4 minimize y^4
y=0
for x=3, x^4=81
for x=4, x^4= 256
so x must be greater than 3 but less than 4
only B satisfies this
The powers of two are bloody impolite!!
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by Nermal » Sun Sep 06, 2009 11:06 pm
I agree with you guys, but I would first take the squareroot of everything.

x^2+y^2=10

if y=0, then x^2=10, x=sqrt10=3,16...
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by sakurle » Mon Sep 07, 2009 9:41 pm
I am not sure I understand your logic. I don't think sqrt(x^4 + y^4) is same as x^2+y^2.
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by Nermal » Tue Sep 08, 2009 12:31 am
Maybe because there was no logic.
Sorry, this was a very stupid mistake!
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