# 4x ^ 2 5x 12 = 0

## Step  1  :

#### Equation at the kết thúc of step  1  :

(22x2 - 5x) - 12 = 0

## Step  2  :

#### Trying lớn factor by splitting the middle term

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2.1     Factoring  4x2-5x-12

The first term is,  4x2  its coefficient is  4 .
The middle term is,  -5x  its coefficient is  -5 .
The last term, "the constant", is  -12

Step-1 : Multiply the coefficient of the first term by the constant   4 • -12 = -48

Step-2 : Find two factors of  -48  whose sum equals the coefficient of the middle term, which is   -5 .

 -48 + 1 = -47 -24 + 2 = -22 -16 + 3 = -13 -12 + 4 = -8 -8 + 6 = -2 -6 + 8 = 2 -4 + 12 = 8 -3 + 16 = 13 -2 + 24 = 22 -1 + 48 = 47

Observation : No two such factors can be found !!
Conclusion : Trinomial can not be factored

#### Equation at the kết thúc of step  2  :

4x2 - 5x - 12 = 0

## Step  3  :

#### Parabola, Finding the Vertex :

3.1      Find the Vertex of   y = 4x2-5x-12Parabolas have a highest or a lowest point called the Vertex .   Our parabola opens up and accordingly has a lowest point (AKA absolute minimum) .   We know this even before plotting  "y"  because the coefficient of the first term, 4 , is positive (greater than thở zero). Each parabola has a vertical line of symmetry that passes through its vertex. Because of this symmetry, the line of symmetry would, for example, pass through the midpoint of the two  x -intercepts (roots or solutions) of the parabola. That is, if the parabola has indeed two real solutions. Parabolas can model many real life situations, such as the height above ground, of an object thrown upward, after some period of time. The vertex of the parabola can provide us with information, such as the maximum height that object, thrown upwards, can reach. For this reason we want lớn be able lớn find the coordinates of the vertex. For any parabola,Ax2+Bx+C,the  x -coordinate of the vertex is given by  -B/(2A) . In our case the  x  coordinate is   0.6250  Plugging into the parabola formula   0.6250  for  x  we can calculate the  y -coordinate :

y = 4.0 * 0.62 * 0.62 - 5.0 * 0.62 - 12.0
or   y = -13.562

#### Parabola, Graphing Vertex and X-Intercepts :

Root plot for :  y = 4x2-5x-12
Axis of Symmetry (dashed)  {x}={ 0.62}
Vertex at  {x,y} = { 0.62,-13.56}
x -Intercepts (Roots) :
Root 1 at  {x,y} = {-1.22, 0.00}
Root 2 at  {x,y} = { 2.47, 0.00}

#### Solve Quadratic Equation by Completing The Square

3.2     Solving   4x2-5x-12 = 0 by Completing The Square .Divide both sides of the equation by  4  to have 1 as the coefficient of the first term :
x2-(5/4)x-3 = 0

Add  3  lớn both side of the equation :
x2-(5/4)x = 3

Now the clever bit: Take the coefficient of  x , which is  5/4 , divide by two, giving  5/8 , and finally square it giving  25/64

Add  25/64  lớn both sides of the equation :
On the right hand side we have :
3  +  25/64    or,  (3/1)+(25/64)
The common denominator of the two fractions is  64   Adding  (192/64)+(25/64)  gives  217/64
So adding lớn both sides we finally get :
x2-(5/4)x+(25/64) = 217/64

Adding  25/64  has completed the left hand side into a perfect square :
x2-(5/4)x+(25/64)  =
(x-(5/8)) • (x-(5/8))  =
(x-(5/8))2
Things which are equal lớn the same thing are also equal lớn one another. Since
x2-(5/4)x+(25/64) = 217/64 and
x2-(5/4)x+(25/64) = (x-(5/8))2
then, according lớn the law of transitivity,
(x-(5/8))2 = 217/64

We'll refer lớn this Equation as  Eq. #3.2.1

The Square Root Principle says that When two things are equal, their square roots are equal.

Note that the square root of
(x-(5/8))2   is
(x-(5/8))2/2 =
(x-(5/8))1 =
x-(5/8)

Now, applying the Square Root Principle to  Eq. #3.2.1  we get:
x-(5/8) = 217/64

Add  5/8  lớn both sides lớn obtain:
x = 5/8 + √ 217/64

Since a square root has two values, one positive and the other negative
x2 - (5/4)x - 3 = 0
has two solutions:
x = 5/8 + √ 217/64
or
x = 5/8 - √ 217/64

Note that  √ 217/64 can be written as
217  / √ 64   which is  217  / 8

3.3     Solving    4x2-5x-12 = 0 by the Quadratic Formula .According lớn the Quadratic Formula,  x  , the solution for   Ax2+Bx+C  = 0  , where  A, B  and  C  are numbers, often called coefficients, is given by :

- B  ±  √ B2-4AC
x =   ————————
2A
In our case,  A   =     4
B   =    -5
C   =  -12
Accordingly,  B2  -  4AC   =
25 - (-192) =
217

5 ± √ 217
x  =    —————
8
√ 217   , rounded lớn 4 decimal digits, is  14.7309
So now we are looking at:
x  =  ( 5 ±  14.731 ) / 8

Two real solutions:

x =(5+√217)/8= 2.466

or:

x =(5-√217)/8=-1.216

## Two solutions were found :

1.  x =(5-√217)/8=-1.216
2.  x =(5+√217)/8= 2.466