Solution - Quadratic equations

Step by step solution :

Step  1  :

Equation at the end of step  1  :

  ((2•5x2) -  247x) +  400  = 0 

Step  2  :

Trying to factor by splitting the middle term

 2.1     Factoring  10x²-247x+400 

The first term is,  10x²  its coefficient is  10 .
The middle term is,  -247x  its coefficient is  -247 .
The last term, "the constant", is  +400 

Step-1 : Multiply the coefficient of the first term by the constant   10 • 400 = 4000 

Step-2 : Find two factors of  4000  whose sum equals the coefficient of the middle term, which is   -247 .

For tidiness, printing of 42 lines which failed to find two such factors, was suppressed

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

Equation at the end of step  2  :

  10x2 - 247x + 400  = 0 

Step  3  :

Parabola, Finding the Vertex :

 3.1      Find the Vertex of   y = 10x²-247x+400

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, 10 , 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  12.3500  

 Plugging into the parabola formula  12.3500  for  x  we can calculate the  y -coordinate : 
  y = 10.0 * 12.35 * 12.35 - 247.0 * 12.35 + 400.0
or   y = -1125.225

Parabola, Graphing Vertex and X-Intercepts :

Root plot for :  y = 10x²-247x+400
Axis of Symmetry (dashed)  {x}={12.35} 
Vertex at  {x,y} = {12.35,-1125.22} 
 x -Intercepts (Roots) :
Root 1 at  {x,y} = { 1.74, 0.00} 
Root 2 at  {x,y} = {22.96, 0.00} 

Solve Quadratic Equation by Completing The Square

 3.2     Solving   10x²-247x+400 = 0 by Completing The Square .

 Divide both sides of the equation by  10  to have 1 as the coefficient of the first term :
   x²-(247/10)x+40 = 0

Subtract  40  from both side of the equation :
   x²-(247/10)x = -40

Now the clever bit: Take the coefficient of  x , which is  247/10 , divide by two, giving  247/20 , and finally square it giving  61009/400 

Add  61009/400  to both sides of the equation :
  On the right hand side we have :
   -40  +  61009/400    or,  (-40/1)+(61009/400) 
  The common denominator of the two fractions is  400   Adding  (-16000/400)+(61009/400)  gives  45009/400 
  So adding to both sides we finally get :
   x²-(247/10)x+(61009/400) = 45009/400

Adding  61009/400  has completed the left hand side into a perfect square :
   x²-(247/10)x+(61009/400)  =
   (x-(247/20)) • (x-(247/20))  =
  (x-(247/20))²
Things which are equal to the same thing are also equal to one another. Since
   x²-(247/10)x+(61009/400) = 45009/400 and
   x²-(247/10)x+(61009/400) = (x-(247/20))²
then, according to the law of transitivity,
   (x-(247/20))² = 45009/400

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-(247/20))²   is
   (x-(247/20))^2/2 =
  (x-(247/20))¹ =
   x-(247/20)

Now, applying the Square Root Principle to  Eq. #3.2.1  we get:
   x-(247/20) = √ 45009/400

Add  247/20  to both sides to obtain:
   x = 247/20 + √ 45009/400

Since a square root has two values, one positive and the other negative
   x² - (247/10)x + 40 = 0
   has two solutions:
  x = 247/20 + √ 45009/400
   or
  x = 247/20 - √ 45009/400

Note that  √ 45009/400 can be written as
  √ 45009  / √ 400   which is √ 45009  / 20

Solve Quadratic Equation using the Quadratic Formula

 3.3     Solving    10x²-247x+400 = 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   =     10
                      B   =   -247
                      C   =  400

Accordingly,  B²  -  4AC   =
                     61009 - 16000 =
                     45009

Applying the quadratic formula :

               247 ± √ 45009
   x  =    ————————
                        20

Can  √ 45009 be simplified ?

Yes!   The prime factorization of  45009   is
   3•3•3•1667 
To be able to remove something from under the radical, there have to be  2  instances of it (because we are taking a square i.e. second root).

√ 45009   =  √ 3•3•3•1667   =
                ±  3 • √ 5001

  √ 5001   , rounded to 4 decimal digits, is  70.7177
 So now we are looking at:
           x  =  ( 247 ± 3 •  70.718 ) / 20

Two real solutions:

 x =(247+√45009)/20=(247+3√ 5001 )/20= 22.958

or:

 x =(247-√45009)/20=(247-3√ 5001 )/20= 1.742

Two solutions were found :

1.  x =(247-√45009)/20=(247-3√ 5001 )/20= 1.742
2.  x =(247+√45009)/20=(247+3√ 5001 )/20= 22.958