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So please: Provide answer choices for PS questions.

Original question is: Given that x^4 – 25x^2 = -144, which of the following is NOT a sum of two possible values of x? A. -7 B. -1 C. 0 D. 3 E. 7

Factor x^4-25x^2+144=0 --> (x^2 - 16)*(x^2 - 9)=0 --> x^2=16 or x^2=9 (alternately you could solve x^4-25x^2+144=0 for x^2 to get the same values for it) --> x=4 or x=-4 or x=3 or x=-3.

All but option D. could be expressed as the sum of two roots: A. 7=-4-3; B. -1=-3+4; C. 0=3-3 (or 0=4-4); E. 7=3+4.

Answer: D.

As for your question: there are no enough answer choices to show all possible values of a sum of two roots, so there are 4 possible values for a sum and one which is not.

So please: Provide answer choices for PS questions.

Original question is: Given that x^4 – 25x^2 = -144, which of the following is NOT a sum of two possible values of x? A. -7 B. -1 C. 0 D. 3 E. 7

Factorx^4-25x^2+144=0 --> (x^2 - 16)*(x^2 - 9)=0 --> x^2=16 or x^2=9 (alternately you could solve x^4-25x^2+144=0 for x^2 to get the same values for it) --> x=4 or x=-4 or x=3 or x=-3.

All but option D. could be expressed as the sum of two roots: A. 7=-4-3; B. -1=-3+4; C. 0=3-3 (or 0=4-4); E. 7=3+4.

Answer: D.

As for your question: there are no enough answer choices to show all possible values of a sum of two roots, so there are 4 possible values for a sum and one which is not.

So please: Provide answer choices for PS questions.

Original question is: Given that x^4 – 25x^2 = -144, which of the following is NOT a sum of two possible values of x? A. -7 B. -1 C. 0 D. 3 E. 7

Factorx^4-25x^2+144=0 --> (x^2 - 16)*(x^2 - 9)=0 --> x^2=16 or x^2=9 (alternately you could solve x^4-25x^2+144=0 for x^2 to get the same values for it) --> x=4 or x=-4 or x=3 or x=-3.

All but option D. could be expressed as the sum of two roots: A. 7=-4-3; B. -1=-3+4; C. 0=3-3 (or 0=4-4); E. 7=3+4.

Answer: D.

As for your question: there are no enough answer choices to show all possible values of a sum of two roots, so there are 4 possible values for a sum and one which is not.

So please: Provide answer choices for PS questions.

Original question is: Given that x^4 – 25x^2 = -144, which of the following is NOT a sum of two possible values of x? A. -7 B. -1 C. 0 D. 3 E. 7

Factorx^4-25x^2+144=0 --> (x^2 - 16)*(x^2 - 9)=0 --> x^2=16 or x^2=9 (alternately you could solve x^4-25x^2+144=0 for x^2 to get the same values for it) --> x=4 or x=-4 or x=3 or x=-3.

All but option D. could be expressed as the sum of two roots: A. 7=-4-3; B. -1=-3+4; C. 0=3-3 (or 0=4-4); E. 7=3+4.

Answer: D.

As for your question: there are no enough answer choices to show all possible values of a sum of two roots, so there are 4 possible values for a sum and one which is not.

Hope it's clear.

How did u calculate the highlighted part.

To calculate the roots of a quadratic equation ax^2+bx+c=0 you can use the formula roots =(-b+sqrt(b^2-4ac))/2a...and .....(-b-sqrt(b^2-4ac))/2a

now in this x^4-25x^2+144=0===>just for convenience put x^2= X therefore equation becomes: X^2-25X+144=0

NOW using the formula of roots

X=(25+sqrt(25^2-4*1*144))/2 and X=(25-sqrt(25^2-4*1*144))/2 On simplifying X=16...AND X=9 now replacing back X WITH x we get x^2=16 and x^2=9 therefore four roots are x=+4,-4,+3,-3

hope it helps...

SKM

hope it h
_________________

When you want to succeed as bad as you want to breathe ...then you will be successfull....

Re: Given that x^4 – 25x^2 = -144, which of the following is NOT [#permalink]
03 Jul 2013, 09:19

1

This post received KUDOS

subhashghosh wrote:

Given that x^4 – 25x^2 = -144, which of the following is NOT a sum of two possible values of x?

A. -7 B. -1 C. 0 D. 3 E. 7

Factorization of roots initially conisder 144 and now diivide this to roots which add to 25 => 16, 9 and now x^2 -9 and x^2 -15 one of them is equal to zero, equate and we get l3l l4l as the roots so add them individually in all combniations we can achieve all othe but not 3 as sum of two roots