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anonymous

  • one year ago

need help !! :))

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  1. anonymous
    • one year ago
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    with?

  2. anonymous
    • one year ago
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  3. phi
    • one year ago
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    line 1 is ok. but line 2 is wrong in other words, (x-y)^2 is *not* x^2-y^2 (which is what they did) (x-y)^2 is x^2 +y^2 -2xy

  4. anonymous
    • one year ago
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    what am i supposed to d then? how do i solve it

  5. phi
    • one year ago
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    You did not post the question. I assume they want to know which line contains a mistake. If so, that would be line 2.

  6. anonymous
    • one year ago
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    i have to find the mistake then solve it correctly

  7. phi
    • one year ago
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    ok. line 1 is technically not a mistake, but it is the wrong first step (line 2 is definitely a mistake) I would start over, with the original \[ x - \sqrt{17-4x}= 3 \] and put the square root on the right-hand side , like this: \[ x - \sqrt{17-4x} +\sqrt{17-4x} = 3 + \sqrt{17-4x} \] the left side simplifies \[ x= 3 + \sqrt{17-4x} \] now add -3 to both sides \[ x-3 = \sqrt{17-4x} \]

  8. phi
    • one year ago
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    now square both sides. on the left that means write (x-3)^2 on the right , what do you get after squaring ? any idea?

  9. anonymous
    • one year ago
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    X^2-6X+9?

  10. phi
    • one year ago
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    yes, that is the left side. the right side is "easy" --- squaring gets rid of the square root side. can you write down the whole equation (both sides)?

  11. anonymous
    • one year ago
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    X^2-6X+9=17-4X

  12. phi
    • one year ago
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    now add -17 to both sides and +4x to both sides

  13. anonymous
    • one year ago
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    X^2-2X-8?

  14. phi
    • one year ago
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    you mean X^2-2X-8=0 remember it is an equation

  15. anonymous
    • one year ago
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    A=1,B=-2,C=-8

  16. phi
    • one year ago
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    yes. you can use the quadratic formula (if they want you to) but you can factor this: notice -4* 2= -8 and -4+2= -2

  17. anonymous
    • one year ago
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    OH YEAH

  18. anonymous
    • one year ago
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    THATS IT? thanks so much!! :)

  19. phi
    • one year ago
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    (x-4)(x+2)= 0 either x-4=0 --> x=4 or x+2 =0 ---> x= -2 however, with these types of problems you have to check both solutions. sometimes you get an "extraneous" solution. So check both values in the original equation

  20. anonymous
    • one year ago
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    -2 is false. thanks:)

  21. phi
    • one year ago
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    yes

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