Solution - Quadratic equations

Step by step solution :

Step  1  :

Trying to factor by splitting the middle term

 1.1     Factoring  x²+200x-15540 

The first term is,  x²  its coefficient is  1 .
The middle term is,  +200x  its coefficient is  200 .
The last term, "the constant", is  -15540 

Step-1 : Multiply the coefficient of the first term by the constant   1 • -15540 = -15540 

Step-2 : Find two factors of  -15540  whose sum equals the coefficient of the middle term, which is   200 .

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  1  :

  x2 + 200x - 15540  = 0 

Step  2  :

Parabola, Finding the Vertex :

 2.1      Find the Vertex of   y = x²+200x-15540

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, 1 , 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  -100.0000  

 Plugging into the parabola formula  -100.0000  for  x  we can calculate the  y -coordinate : 
  y = 1.0 * -100.00 * -100.00 + 200.0 * -100.00 - 15540.0
or   y = -25540.000

Parabola, Graphing Vertex and X-Intercepts :

Root plot for :  y = x²+200x-15540
Axis of Symmetry (dashed)  {x}={-100.00} 
Vertex at  {x,y} = {-100.00,-25540.00} 
 x -Intercepts (Roots) :
Root 1 at  {x,y} = {-259.81, 0.00} 
Root 2 at  {x,y} = {59.81, 0.00} 

Solve Quadratic Equation by Completing The Square

 2.2     Solving   x²+200x-15540 = 0 by Completing The Square .

 Add  15540  to both side of the equation :
   x²+200x = 15540

Now the clever bit: Take the coefficient of  x , which is  200 , divide by two, giving  100 , and finally square it giving  10000 

Add  10000  to both sides of the equation :
  On the right hand side we have :
   15540  +  10000    or,  (15540/1)+(10000/1) 
  The common denominator of the two fractions is  1   Adding  (15540/1)+(10000/1)  gives  25540/1 
  So adding to both sides we finally get :
   x²+200x+10000 = 25540

Adding  10000  has completed the left hand side into a perfect square :
   x²+200x+10000  =
   (x+100) • (x+100)  =
  (x+100)²
Things which are equal to the same thing are also equal to one another. Since
   x²+200x+10000 = 25540 and
   x²+200x+10000 = (x+100)²
then, according to the law of transitivity,
   (x+100)² = 25540

We'll refer to this Equation as  Eq. #2.2.1  

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

Note that the square root of
   (x+100)²   is
   (x+100)^2/2 =
  (x+100)¹ =
   x+100

Now, applying the Square Root Principle to  Eq. #2.2.1  we get:
   x+100 = √ 25540

Subtract  100  from both sides to obtain:
   x = -100 + √ 25540

Since a square root has two values, one positive and the other negative
   x² + 200x - 15540 = 0
   has two solutions:
  x = -100 + √ 25540
   or
  x = -100 - √ 25540

Solve Quadratic Equation using the Quadratic Formula

 2.3     Solving    x²+200x-15540 = 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   =     1
                      B   =   200
                      C   =  -15540

Accordingly,  B²  -  4AC   =
                     40000 - (-62160) =
                     102160

Applying the quadratic formula :

               -200 ± √ 102160
   x  =    —————————
                          2

Can  √ 102160 be simplified ?

Yes!   The prime factorization of  102160   is
   2•2•2•2•5•1277 
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).

√ 102160   =  √ 2•2•2•2•5•1277   =2•2•√ 6385   =
                ±  4 • √ 6385

  √ 6385   , rounded to 4 decimal digits, is  79.9062
 So now we are looking at:
           x  =  ( -200 ± 4 •  79.906 ) / 2

Two real solutions:

 x =(-200+√102160)/2=-100+2√ 6385 = 59.812

or:

 x =(-200-√102160)/2=-100-2√ 6385 = -259.812

Two solutions were found :

1.  x =(-200-√102160)/2=-100-2√ 6385 = -259.812
2.  x =(-200+√102160)/2=-100+2√ 6385 = 59.812