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3y^2+31y+36

 Oct 19, 2015
 #1
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3y^2+31y+36

 

Solve for y over the real numbers:
3 y^2+31 y+36 = 0

The left hand side factors into a product with two terms:
(y+9) (3 y+4) = 0

Split into two equations:
y+9 = 0 or 3 y+4 = 0

Subtract 9 from both sides:
y = -9 or 3 y+4 = 0

Subtract 4 from both sides:
y = -9 or 3 y = -4

Divide both sides by 3:
Answer: | 
| y = -9 or y = -4/3

 Oct 19, 2015
 #2
avatar+118723 
+5

3y^2+31y+36

 

I am sorry guest but your answer is NOT correct.

 

There is no equal sign here, this is NOT an equation.  So you have answered a different question entirely!

 

The question is, how do you factor    \(3y^2+31y+36\).

 

 

What you need to look for is two numbers that multiply to 3*36  and add to 31

 

Since both these numbersare positive, both the numbers that you are looking for will also be positive.

 

Factors of 3*36 

=3*3*12

=3*3*3*4

=3*3*3*2*2

=  27 * 4

and 27+4=31 so these are the numbers that I want.

So now I have to repleace  31y   with    27y+4      like this

 

 

\(\quad3y^2+31y+36\\ =​​​​3y^2+27y+4y+36\\ \mbox{Now I have to factor in pairs}\\ =3y(y+9)+4(y+9)\\ =(3y+4)(y+9)\)

 

If you do not understand say so :))

 Oct 19, 2015

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