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You are here: Home / Official GMAT Guides / 2018 Official GMAT Guide /

Question 366 Data Sufficiency 2018 GMAT Official Guide

Question 366 Data Sufficiency 2018 GMAT Official Guide

 
Video explanation: If r and s are roots of the equation $x^2+bx+c=0$, where b…

Comments

  1. Josh says

    May 30, 2019 at 3:25 PM

    I believe your concepts are correct. Just one thing to note is that the original quadratic equation in the question is x^2 + Bx + C = 0.

    And then your second step is (x – R)( x – S). However, I think it should have been (x + R)(x +S) in order for it to mimic the first question exactly.

    Let me know if my logic is flawed? It might be that R and S could be negative but I guess we wouldn’t know that.

    Reply
    • GMAT Quantum says

      May 30, 2019 at 5:59 PM

      Hi Josh,

      In general if the roots of a quadratic are given as $r$ and $s$, then the $(x-r)$ and $(x-s)$ are the factors of the quadratic equation, and not $(x+r)$ and $(x+s)$. This is because if we replace $x$ with $r$, then the expression needs to equal zero, which will not be the case if the quadratic is written as $(x+r)(x+s)$. I hope this makes sense.

      Dabral

      Reply

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