Solution - Quadratic equations

Step by step solution :

Step  1  :

Trying to factor by splitting the middle term

 1.1     Factoring  k²+300k-20000 

The first term is,  k²  its coefficient is  1 .
The middle term is,  +300k  its coefficient is  300 .
The last term, "the constant", is  -20000 

Step-1 : Multiply the coefficient of the first term by the constant   1 • -20000 = -20000 

Step-2 : Find two factors of  -20000  whose sum equals the coefficient of the middle term, which is   300 .

For tidiness, printing of 24 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  :

  k2 + 300k - 20000  = 0 

Step  2  :

Parabola, Finding the Vertex :

 2.1      Find the Vertex of   y = k²+300k-20000

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,Ak²+Bk+C,the  k -coordinate of the vertex is given by  -B/(2A) . In our case the  k  coordinate is  -150.0000  

 Plugging into the parabola formula  -150.0000  for  k  we can calculate the  y -coordinate : 
  y = 1.0 * -150.00 * -150.00 + 300.0 * -150.00 - 20000.0
or   y = -42500.000

Parabola, Graphing Vertex and X-Intercepts :

Root plot for :  y = k²+300k-20000
Axis of Symmetry (dashed)  {k}={-150.00} 
Vertex at  {k,y} = {-150.00,-42500.00} 
 k -Intercepts (Roots) :
Root 1 at  {k,y} = {-356.16, 0.00} 
Root 2 at  {k,y} = {56.16, 0.00} 

Solve Quadratic Equation by Completing The Square

 2.2     Solving   k²+300k-20000 = 0 by Completing The Square .

 Add  20000  to both side of the equation :
   k²+300k = 20000

Now the clever bit: Take the coefficient of  k , which is  300 , divide by two, giving  150 , and finally square it giving  22500 

Add  22500  to both sides of the equation :
  On the right hand side we have :
   20000  +  22500    or,  (20000/1)+(22500/1) 
  The common denominator of the two fractions is  1   Adding  (20000/1)+(22500/1)  gives  42500/1 
  So adding to both sides we finally get :
   k²+300k+22500 = 42500

Adding  22500  has completed the left hand side into a perfect square :
   k²+300k+22500  =
   (k+150) • (k+150)  =
  (k+150)²
Things which are equal to the same thing are also equal to one another. Since
   k²+300k+22500 = 42500 and
   k²+300k+22500 = (k+150)²
then, according to the law of transitivity,
   (k+150)² = 42500

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
   (k+150)²   is
   (k+150)^2/2 =
  (k+150)¹ =
   k+150

Now, applying the Square Root Principle to  Eq. #2.2.1  we get:
   k+150 = √ 42500

Subtract  150  from both sides to obtain:
   k = -150 + √ 42500

Since a square root has two values, one positive and the other negative
   k² + 300k - 20000 = 0
   has two solutions:
  k = -150 + √ 42500
   or
  k = -150 - √ 42500

Solve Quadratic Equation using the Quadratic Formula

 2.3     Solving    k²+300k-20000 = 0 by the Quadratic Formula .

 According to the Quadratic Formula,  k  , the solution for   Ak²+Bk+C  = 0  , where  A, B  and  C  are numbers, often called coefficients, is given by :
                                     
            - B  ±  √ B²-4AC
  k =   ————————
                      2A

  In our case,  A   =     1
                      B   =   300
                      C   =  -20000

Accordingly,  B²  -  4AC   =
                     90000 - (-80000) =
                     170000

Applying the quadratic formula :

               -300 ± √ 170000
   k  =    —————————
                          2

Can  √ 170000 be simplified ?

Yes!   The prime factorization of  170000   is
   2•2•2•2•5•5•5•5•17 
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).

√ 170000   =  √ 2•2•2•2•5•5•5•5•17   =2•2•5•5•√ 17   =
                ±  100 • √ 17

  √ 17   , rounded to 4 decimal digits, is   4.1231
 So now we are looking at:
           k  =  ( -300 ± 100 •  4.123 ) / 2

Two real solutions:

 k =(-300+√170000)/2=-150+50√ 17 = 56.155

or:

 k =(-300-√170000)/2=-150-50√ 17 = -356.155

Two solutions were found :

1.  k =(-300-√170000)/2=-150-50√ 17 = -356.155
2.  k =(-300+√170000)/2=-150+50√ 17 = 56.155