Solution - Quadratic equations

Step by step solution :

Step  1  :

Equation at the end of step  1  :

  ((2•5k2) -  19k) -  6  = 0 

Step  2  :

Trying to factor by splitting the middle term

 2.1     Factoring  10k²-19k-6 

The first term is,  10k²  its coefficient is  10 .
The middle term is,  -19k  its coefficient is  -19 .
The last term, "the constant", is  -6 

Step-1 : Multiply the coefficient of the first term by the constant   10 • -6 = -60 

Step-2 : Find two factors of  -60  whose sum equals the coefficient of the middle term, which is   -19 .

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

Equation at the end of step  2  :

  10k2 - 19k - 6  = 0 

Step  3  :

Parabola, Finding the Vertex :

 3.1      Find the Vertex of   y = 10k²-19k-6

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,Ak²+Bk+C,the  k -coordinate of the vertex is given by  -B/(2A) . In our case the  k  coordinate is   0.9500  

 Plugging into the parabola formula   0.9500  for  k  we can calculate the  y -coordinate : 
  y = 10.0 * 0.95 * 0.95 - 19.0 * 0.95 - 6.0
or   y = -15.025

Parabola, Graphing Vertex and X-Intercepts :

Root plot for :  y = 10k²-19k-6
Axis of Symmetry (dashed)  {k}={ 0.95} 
Vertex at  {k,y} = { 0.95,-15.03} 
 k -Intercepts (Roots) :
Root 1 at  {k,y} = {-0.28, 0.00} 
Root 2 at  {k,y} = { 2.18, 0.00} 

Solve Quadratic Equation by Completing The Square

 3.2     Solving   10k²-19k-6 = 0 by Completing The Square .

 Divide both sides of the equation by  10  to have 1 as the coefficient of the first term :
   k²-(19/10)k-(3/5) = 0

Add  3/5  to both side of the equation :
   k²-(19/10)k = 3/5

Now the clever bit: Take the coefficient of  k , which is  19/10 , divide by two, giving  19/20 , and finally square it giving  361/400 

Add  361/400  to both sides of the equation :
  On the right hand side we have :
   3/5  +  361/400   The common denominator of the two fractions is  400   Adding  (240/400)+(361/400)  gives  601/400 
  So adding to both sides we finally get :
   k²-(19/10)k+(361/400) = 601/400

Adding  361/400  has completed the left hand side into a perfect square :
   k²-(19/10)k+(361/400)  =
   (k-(19/20)) • (k-(19/20))  =
  (k-(19/20))²
Things which are equal to the same thing are also equal to one another. Since
   k²-(19/10)k+(361/400) = 601/400 and
   k²-(19/10)k+(361/400) = (k-(19/20))²
then, according to the law of transitivity,
   (k-(19/20))² = 601/400

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
   (k-(19/20))²   is
   (k-(19/20))^2/2 =
  (k-(19/20))¹ =
   k-(19/20)

Now, applying the Square Root Principle to  Eq. #3.2.1  we get:
   k-(19/20) = √ 601/400

Add  19/20  to both sides to obtain:
   k = 19/20 + √ 601/400

Since a square root has two values, one positive and the other negative
   k² - (19/10)k - (3/5) = 0
   has two solutions:
  k = 19/20 + √ 601/400
   or
  k = 19/20 - √ 601/400

Note that  √ 601/400 can be written as
  √ 601  / √ 400   which is √ 601  / 20

Solve Quadratic Equation using the Quadratic Formula

 3.3     Solving    10k²-19k-6 = 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   =     10
                      B   =   -19
                      C   =   -6

Accordingly,  B²  -  4AC   =
                     361 - (-240) =
                     601

Applying the quadratic formula :

               19 ± √ 601
   k  =    ——————
                      20

  √ 601   , rounded to 4 decimal digits, is  24.5153
 So now we are looking at:
           k  =  ( 19 ±  24.515 ) / 20

Two real solutions:

 k =(19+√601)/20= 2.176

or:

 k =(19-√601)/20=-0.276

Two solutions were found :

1.  k =(19-√601)/20=-0.276
2.  k =(19+√601)/20= 2.176