Solution - Quadratic equations

Step by step solution :

Step  1  :

Equation at the end of step  1  :

  ((2•5x2) +  3500x) -  66000  = 0 

Step  2  :

Step  3  :

Pulling out like terms :

 3.1     Pull out like factors :

   10x² + 3500x - 66000  =   10 • (x² + 350x - 6600) 

Trying to factor by splitting the middle term

 3.2     Factoring  x² + 350x - 6600 

The first term is,  x²  its coefficient is  1 .
The middle term is,  +350x  its coefficient is  350 .
The last term, "the constant", is  -6600 

Step-1 : Multiply the coefficient of the first term by the constant   1 • -6600 = -6600 

Step-2 : Find two factors of  -6600  whose sum equals the coefficient of the middle term, which is   350 .

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  3  :

  10 • (x2 + 350x - 6600)  = 0 

Step  4  :

Equations which are never true :

 4.1      Solve :    10   =  0

This equation has no solution.
A a non-zero constant never equals zero.

Parabola, Finding the Vertex :

 4.2      Find the Vertex of   y = x²+350x-6600

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  -175.0000  

 Plugging into the parabola formula  -175.0000  for  x  we can calculate the  y -coordinate : 
  y = 1.0 * -175.00 * -175.00 + 350.0 * -175.00 - 6600.0
or   y = -37225.000

Parabola, Graphing Vertex and X-Intercepts :

Root plot for :  y = x²+350x-6600
Axis of Symmetry (dashed)  {x}={-175.00} 
Vertex at  {x,y} = {-175.00,-37225.00} 
 x -Intercepts (Roots) :
Root 1 at  {x,y} = {-367.94, 0.00} 
Root 2 at  {x,y} = {17.94, 0.00} 

Solve Quadratic Equation by Completing The Square

 4.3     Solving   x²+350x-6600 = 0 by Completing The Square .

 Add  6600  to both side of the equation :
   x²+350x = 6600

Now the clever bit: Take the coefficient of  x , which is  350 , divide by two, giving  175 , and finally square it giving  30625 

Add  30625  to both sides of the equation :
  On the right hand side we have :
   6600  +  30625    or,  (6600/1)+(30625/1) 
  The common denominator of the two fractions is  1   Adding  (6600/1)+(30625/1)  gives  37225/1 
  So adding to both sides we finally get :
   x²+350x+30625 = 37225

Adding  30625  has completed the left hand side into a perfect square :
   x²+350x+30625  =
   (x+175) • (x+175)  =
  (x+175)²
Things which are equal to the same thing are also equal to one another. Since
   x²+350x+30625 = 37225 and
   x²+350x+30625 = (x+175)²
then, according to the law of transitivity,
   (x+175)² = 37225

We'll refer to this Equation as  Eq. #4.3.1  

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

Note that the square root of
   (x+175)²   is
   (x+175)^2/2 =
  (x+175)¹ =
   x+175

Now, applying the Square Root Principle to  Eq. #4.3.1  we get:
   x+175 = √ 37225

Subtract  175  from both sides to obtain:
   x = -175 + √ 37225

Since a square root has two values, one positive and the other negative
   x² + 350x - 6600 = 0
   has two solutions:
  x = -175 + √ 37225
   or
  x = -175 - √ 37225

Solve Quadratic Equation using the Quadratic Formula

 4.4     Solving    x²+350x-6600 = 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   =   350
                      C   =  -6600

Accordingly,  B²  -  4AC   =
                     122500 - (-26400) =
                     148900

Applying the quadratic formula :

               -350 ± √ 148900
   x  =    —————————
                          2

Can  √ 148900 be simplified ?

Yes!   The prime factorization of  148900   is
   2•2•5•5•1489 
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).

√ 148900   =  √ 2•2•5•5•1489   =2•5•√ 1489   =
                ±  10 • √ 1489

  √ 1489   , rounded to 4 decimal digits, is  38.5876
 So now we are looking at:
           x  =  ( -350 ± 10 •  38.588 ) / 2

Two real solutions:

 x =(-350+√148900)/2=-175+5√ 1489 = 17.938

or:

 x =(-350-√148900)/2=-175-5√ 1489 = -367.938

Two solutions were found :

1.  x =(-350-√148900)/2=-175-5√ 1489 = -367.938
2.  x =(-350+√148900)/2=-175+5√ 1489 = 17.938