anonymous
  • anonymous
Gabby solve {x^2} - x - 20 = 0 as shown below: \begin{array}{l}{x^2} - x - 20 = 0\\\left( {x - 5} \right)\left( {x + 4} \right) = 0\\x = - 5,4\end{array} Caitlyn says Gabby is wrong and believe this is the solution: \begin{array}{l}{x^2} - x - 20 = 0\\\left( {x - 5} \right)\left( {x + 4} \right) = 0\\x = 5, - 4\end{array} Is Gabby or Caitlyn correct? Explain the error made by the incorrect girl.
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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schrodinger
  • schrodinger
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SolomonZelman
  • SolomonZelman
Well, first we have to know that when we say `a•b=0` (in general) THEN, either a or b has to be equal to 0. is this information correct?
anonymous
  • anonymous
by correct you mean the way it was typed ?
SolomonZelman
  • SolomonZelman
I mean that the point I made (as regards to the math part)

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SolomonZelman
  • SolomonZelman
that the point I made is correct or not
anonymous
  • anonymous
{x^2} - x - 20 = 0 this is the problem they are working out
SolomonZelman
  • SolomonZelman
yes, yes, I know.... I am asking you if you are {familiar with/ understand the} the zero product property
anonymous
  • anonymous
not really
SolomonZelman
  • SolomonZelman
You know if you say `x • y = 0` then for it to be true, either x=0, or y=0
SolomonZelman
  • SolomonZelman
Right?
anonymous
  • anonymous
yes
SolomonZelman
  • SolomonZelman
Ok, now back to our problem....
SolomonZelman
  • SolomonZelman
he factored the quadratic equation, and now he has: \(\large\color{black}{ \displaystyle (x-5)(x+4)=0 }\)
SolomonZelman
  • SolomonZelman
Then, this "zero product property" (as I showed with `y•x=0`) has to work here too.
SolomonZelman
  • SolomonZelman
That means that either x-5 =0 or that x+4 =0 Correct or not?
SolomonZelman
  • SolomonZelman
Now, for what value of x is x-5=0? And for what value of x is x+4=0?
anonymous
  • anonymous
it would be 4, and 5 ?
SolomonZelman
  • SolomonZelman
Please in order, and please try again
anonymous
  • anonymous
it would be -5, 4
SolomonZelman
  • SolomonZelman
x-5=0 x+4=0 (-5)-5=0 (4)+4=0 according to what you said:
anonymous
  • anonymous
so the property that they did wrong was the zero property
SolomonZelman
  • SolomonZelman
who did wrong?
anonymous
  • anonymous
Caitlyn and Gabby
SolomonZelman
  • SolomonZelman
One of them is correct. (But only one is correct, the other is wrong)
triciaal
  • triciaal
|dw:1437049882899:dw|
anonymous
  • anonymous
so would Gabby be correcr ?
triciaal
  • triciaal
|dw:1437050014096:dw|
anonymous
  • anonymous
so it would be Catilyn who is right ?
SolomonZelman
  • SolomonZelman
|dw:1437050054286:dw|
SolomonZelman
  • SolomonZelman
it seems as though you are trying to guess the answer....
anonymous
  • anonymous
x= -4 and x=5
SolomonZelman
  • SolomonZelman
yes
SolomonZelman
  • SolomonZelman
x=-4, x=5 that is correct

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