Quadratic Equation - Simple

  • Thread starter Larrytsai
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  • #1
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I know this is a simple question but for some reason im getting stumped:

Question: x-3=-x^2
atempt: (x^2)+x = 3

x^2 + x + 1/4= 3(4) + 1/4

(x+1/2)^2= 3

root everthing

x+1/2= root 3
x=+,- root 3 -1/2
 

Answers and Replies

  • #2
symbolipoint
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Your initial algebraic steps were wrong. From the start, you should obtain:

EDIT: bad information was HERE.

from which the solutions are very plain (what?).
 
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  • #3
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-1x2 = 3???
 
  • #4
symbolipoint
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Trying again: Your first steps were wrong. You should first obtain

[tex] \[
x^2 + x - 3 = 0
\]
[/tex]

and then you can use general solution to quadratic equation OR complete square.
 
  • #5
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Well, i don't really understand what u tried to do.

[tex] x-3=-x^{2}=> x^{2}+x-3=0[/tex] Now do you could either try to factor this out, or apply directly the quadratic formula, do you know it?

[tex]x_1_,_2=\frac{-b\pm\sqrt{b^{2}-4ac}}{2a}[/tex]

In this particular case, i don't think it will factor nicely, so it is better to use the quadratic formula i provided u with.
Can u go from here?
 
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  • #6
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sry im only in gr 11 and this was how i was taught... and that formula was never taught to me
 
  • #7
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sry im only in gr 11 and this was how i was taught... and that formula was never taught to me
Well, you better learn it then, because not always will you be able to factor a quadratic eq. nicely.

The general form of a quadratic equation is

[tex] ax^{2}+bx+c=0[/tex] so now can you figure out what a,b and c are in your problem?
 
  • #8
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oo i do know that thats the form i write my solution as, but for my question i stated above i dont know what im doing wrong to keep me from reaching that formula
 
  • #9
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oo i do know that thats the form i write my solution as, but for my question i stated above i dont know what im doing wrong to keep me from reaching that formula
Aha i gotch ya!

[tex]x^2 + x = 3=>x^{2}+2x\frac{1}{2}+\frac{1}{4}-\frac{1}{4}=3=>(x+\frac{1}{2})^{2}=3+\frac{1}{4}=>(x+\frac{1}{2})^{2}=\frac{13}{4}[/tex]

You forgot to add that 1/4 to the 3 on your right hand side.
Well, now you know what to do right?
 
  • #10
Integral
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I know this is a simple question but for some reason im getting stumped:

Question: x-3=-x^2
atempt: (x^2)+x = 3

x^2 + x + 1/4= 3(4) + 1/4

(x+1/2)^2= 3

root everthing

x+1/2= root 3
x=+,- root 3 -1/2
Where did the bolded factor of 4 come from?

You should have.

[tex] (x+ \frac 1 2)^2 = 3 \frac 1 4 [/tex]
 
  • #11
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that was just multiplying the denominator by 4 so i could add fractions
 
  • #12
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that was just multiplying the denominator by 4 so i could add fractions
Well you should have multiplied then both the denominator and the numerator by 4.
 
  • #13
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yea i know i just was too lazy to type it out >.<
 
  • #14
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yea i know i just was too lazy to type it out >.<
Well, that's why you got the wrong result then. Better not be lazy!
 

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