Solution - Quadratic equations

Step by step solution :

Step  1  :

Equation at the end of step  1  :

  ((5•72x2) -  5x) -  2  = 0 

Step  2  :

Trying to factor by splitting the middle term

 2.1     Factoring  245x²-5x-2 

The first term is,  245x²  its coefficient is  245 .
The middle term is,  -5x  its coefficient is  -5 .
The last term, "the constant", is  -2 

Step-1 : Multiply the coefficient of the first term by the constant   245 • -2 = -490 

Step-2 : Find two factors of  -490  whose sum equals the coefficient of the middle term, which is   -5 .

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

Equation at the end of step  2  :

  245x2 - 5x - 2  = 0 

Step  3  :

Parabola, Finding the Vertex :

 3.1      Find the Vertex of   y = 245x²-5x-2

Parabolas 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, 245 , is positive (greater than 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 to be able to 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   0.0102  

 Plugging into the parabola formula   0.0102  for  x  we can calculate the  y -coordinate : 
  y = 245.0 * 0.01 * 0.01 - 5.0 * 0.01 - 2.0
or   y = -2.026

Parabola, Graphing Vertex and X-Intercepts :

Root plot for :  y = 245x²-5x-2
Axis of Symmetry (dashed)  {x}={ 0.01} 
Vertex at  {x,y} = { 0.01,-2.03} 
 x -Intercepts (Roots) :
Root 1 at  {x,y} = {-0.08, 0.00} 
Root 2 at  {x,y} = { 0.10, 0.00} 

Solve Quadratic Equation by Completing The Square

 3.2     Solving   245x²-5x-2 = 0 by Completing The Square .

 Divide both sides of the equation by  245  to have 1 as the coefficient of the first term :
   x²-(1/49)x-(2/245) = 0

Add  2/245  to both side of the equation :
   x²-(1/49)x = 2/245

Now the clever bit: Take the coefficient of  x , which is  1/49 , divide by two, giving  1/98 , and finally square it giving  1/9604 

Add  1/9604  to both sides of the equation :
  On the right hand side we have :
   2/245  +  1/9604   The common denominator of the two fractions is  48020   Adding  (392/48020)+(5/48020)  gives  397/48020 
  So adding to both sides we finally get :
   x²-(1/49)x+(1/9604) = 397/48020

Adding  1/9604  has completed the left hand side into a perfect square :
   x²-(1/49)x+(1/9604)  =
   (x-(1/98)) • (x-(1/98))  =
  (x-(1/98))²
Things which are equal to the same thing are also equal to one another. Since
   x²-(1/49)x+(1/9604) = 397/48020 and
   x²-(1/49)x+(1/9604) = (x-(1/98))²
then, according to the law of transitivity,
   (x-(1/98))² = 397/48020

We'll refer to 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-(1/98))²   is
   (x-(1/98))^2/2 =
  (x-(1/98))¹ =
   x-(1/98)

Now, applying the Square Root Principle to  Eq. #3.2.1  we get:
   x-(1/98) = √ 397/48020

Add  1/98  to both sides to obtain:
   x = 1/98 + √ 397/48020

Since a square root has two values, one positive and the other negative
   x² - (1/49)x - (2/245) = 0
   has two solutions:
  x = 1/98 + √ 397/48020
   or
  x = 1/98 - √ 397/48020

Note that  √ 397/48020 can be written as
  √ 397  / √ 48020 

Solve Quadratic Equation using the Quadratic Formula

 3.3     Solving    245x²-5x-2 = 0 by the Quadratic Formula .

 According to 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   =    245
                      B   =    -5
                      C   =   -2

Accordingly,  B²  -  4AC   =
                     25 - (-1960) =
                     1985

Applying the quadratic formula :

               5 ± √ 1985
   x  =    ——————
                      490

  √ 1985   , rounded to 4 decimal digits, is  44.5533
 So now we are looking at:
           x  =  ( 5 ±  44.553 ) / 490

Two real solutions:

 x =(5+√1985)/490=1/98+1/490√ 1985 = 0.101

or:

 x =(5-√1985)/490=1/98-1/490√ 1985 = -0.081

Two solutions were found :

1.  x =(5-√1985)/490=1/98-1/490√ 1985 = -0.081
2.  x =(5+√1985)/490=1/98+1/490√ 1985 = 0.101