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March 28, 2017

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Solve by completing the square.

5x^2+10x-7=0
My answer: x= -1+ or - 2sqrt.of 10 all over 5

  • Algebra 2 .. - ,

    divide by 5
    x^2 + 2x + ... = 7 + ...
    x^2 + 2x + 1= 7 + 1
    (x+1)^2 = 8
    x+1 = ± √8 = ± 2√2

    x = -1 ± 2√2

  • oops - Algebra 2 .. - ,

    forgot to divide the 7 by 5
    x^2 + 2x + 1 = 7/5 + 1 = 12/5
    (x+1)^2 = ±√12/√5 = ± √60/5 = ± 2√15/5

    x = -1 ± 2√15/5
    x = (-5 ± 2√15)/5

  • Algebra 2 .. - ,

    I do not get it. Here let me show my work.
    5x^2+10x-7=0
    5(x^2+2x+1)-7-1
    5(x+1)^2-8=0
    5(x+1)^2=8
    (x+1)^2=+/- sqrt of 8/5
    (x+1)=+/- 2sqrt of 2 over sqrt of 5
    (x+1)=+/- 2sqrt of 10 over 5
    x= -1+/- 2sqrt of 10 all over 5

  • Algebra 2 .. - ,

    WAIT NEVER MIND.....
    MY FINAL ANSWER IS X=-1+/-2 SQRT OF 15 ALL OVER 5

  • Algebra 2 .. - ,

    But why is your answer x=-5+/- 2sqrt of 15 all over 5?

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