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Solve for y

4y2-5=12y

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Vivian L. | Microsoft Word/Excel/Outlook, essay composition, math; I LOVE TO TEACHMicrosoft Word/Excel/Outlook, essay comp...
3.0 3.0 (1 lesson ratings) (1)
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Hi Lila;
4y2-5=12y
Let's have everything on one side...
4y2-12y-5=0
(2y-3)(2y-3)
Let's FOIL...
FIRST...(2y)(2y)=4y2
OUTER...(2y)(-3)=-6y
INNER...(-3)(2y)=-6y
LAST...(-3)(-3)=9
4y2-6y-6y+9
4y2-12y+9
Obviously, the constant we want is NOT +9.  We want -5...
-5=9-14
4y2-12y+9-14=0
(2y-3)2-14=0
(2y-3)2=14
Square-root both sides...
2y-3=+√14.......2y-3=-√14
2y=3+√14........2y=3-√14
y=(3+√14)/2....y=(3-√14)/2
Tom F. | Math Tutor - I can help you achieve success in mathMath Tutor - I can help you achieve succ...
5.0 5.0 (54 lesson ratings) (54)
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4y^2 - 5 = 12y
 
4y^2 -12y - 5 = 0
 
(2y -5)(2y -1 ) = 0
 
2y - 5 = 0
2y = 5
y = 5/2
 
and
 
2y -1 =0
2y = 1
y = 1/2

Comments

Hi Tom;
In the FOIL, (-5)(-1)=+5, NOT -5.