Solution - Quadratic equations

Rearrange:

Rearrange the equation by subtracting what is to the right of the equal sign from both sides of the equation :

                     26*n^2+41*n+20-(6*n)=0 

Step by step solution :

Step  1  :

Equation at the end of step  1  :

  (((2•13n2) +  41n) +  20) -  6n  = 0 

Step  2  :

Trying to factor by splitting the middle term

 2.1     Factoring  26n²+35n+20 

The first term is,  26n²  its coefficient is  26 .
The middle term is,  +35n  its coefficient is  35 .
The last term, "the constant", is  +20 

Step-1 : Multiply the coefficient of the first term by the constant   26 • 20 = 520 

Step-2 : Find two factors of  520  whose sum equals the coefficient of the middle term, which is   35 .

For tidiness, printing of 26 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  :

  26n2 + 35n + 20  = 0 

Step  3  :

Parabola, Finding the Vertex :

 3.1      Find the Vertex of   y = 26n²+35n+20

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, 26 , 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,An²+Bn+C,the  n -coordinate of the vertex is given by  -B/(2A) . In our case the  n  coordinate is  -0.6731  

 Plugging into the parabola formula  -0.6731  for  n  we can calculate the  y -coordinate : 
  y = 26.0 * -0.67 * -0.67 + 35.0 * -0.67 + 20.0
or   y = 8.221

Parabola, Graphing Vertex and X-Intercepts :

Root plot for :  y = 26n²+35n+20
Axis of Symmetry (dashed)  {n}={-0.67} 
Vertex at  {n,y} = {-0.67, 8.22} 
Function has no real roots

Solve Quadratic Equation by Completing The Square

 3.2     Solving   26n²+35n+20 = 0 by Completing The Square .

 Divide both sides of the equation by  26  to have 1 as the coefficient of the first term :
   n²+(35/26)n+(10/13) = 0

Subtract  10/13  from both side of the equation :
   n²+(35/26)n = -10/13

Now the clever bit: Take the coefficient of  n , which is  35/26 , divide by two, giving  35/52 , and finally square it giving  1225/2704 

Add  1225/2704  to both sides of the equation :
  On the right hand side we have :
   -10/13  +  1225/2704   The common denominator of the two fractions is  2704   Adding  (-2080/2704)+(1225/2704)  gives  -855/2704 
  So adding to both sides we finally get :
   n²+(35/26)n+(1225/2704) = -855/2704

Adding  1225/2704  has completed the left hand side into a perfect square :
   n²+(35/26)n+(1225/2704)  =
   (n+(35/52)) • (n+(35/52))  =
  (n+(35/52))²
Things which are equal to the same thing are also equal to one another. Since
   n²+(35/26)n+(1225/2704) = -855/2704 and
   n²+(35/26)n+(1225/2704) = (n+(35/52))²
then, according to the law of transitivity,
   (n+(35/52))² = -855/2704

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
   (n+(35/52))²   is
   (n+(35/52))^2/2 =
  (n+(35/52))¹ =
   n+(35/52)

Now, applying the Square Root Principle to  Eq. #3.2.1  we get:
   n+(35/52) = √ -855/2704

Subtract  35/52  from both sides to obtain:
   n = -35/52 + √ -855/2704
In Math,  i  is called the imaginary unit. It satisfies   i²  =-1. Both   i   and   -i   are the square roots of   -1 


Since a square root has two values, one positive and the other negative
   n² + (35/26)n + (10/13) = 0
   has two solutions:
  n = -35/52 + √ 855/2704 •  i 
   or
  n = -35/52 - √ 855/2704 •  i 

Note that  √ 855/2704 can be written as
  √ 855  / √ 2704   which is √ 855  / 52

Solve Quadratic Equation using the Quadratic Formula

 3.3     Solving    26n²+35n+20 = 0 by the Quadratic Formula .

 According to the Quadratic Formula,  n  , the solution for   An²+Bn+C  = 0  , where  A, B  and  C  are numbers, often called coefficients, is given by :
                                     
            - B  ±  √ B²-4AC
  n =   ————————
                      2A

  In our case,  A   =     26
                      B   =    35
                      C   =   20

Accordingly,  B²  -  4AC   =
                     1225 - 2080 =
                     -855

Applying the quadratic formula :

               -35 ± √ -855
   n  =    ———————
                        52

In the set of real numbers, negative numbers do not have square roots. A new set of numbers, called complex, was invented so that negative numbers would have a square root. These numbers are written  (a+b*i) 

Both   i   and   -i   are the square roots of minus 1

Accordingly,√ -855  = 
                    √ 855 • (-1)  =
                    √ 855  • √ -1   =
                    ±  √ 855  • i

Can  √ 855 be simplified ?

Yes!   The prime factorization of  855   is
   3•3•5•19 
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).

√ 855   =  √ 3•3•5•19   =
                ±  3 • √ 95

  √ 95   , rounded to 4 decimal digits, is   9.7468
 So now we are looking at:
           n  =  ( -35 ± 3 •  9.747 i ) / 52

Two imaginary solutions :

 n =(-35+√-855)/52=(-35+3i√ 95 )/52= -0.6731+0.5623i
  or: 
 n =(-35-√-855)/52=(-35-3i√ 95 )/52= -0.6731-0.5623i

Two solutions were found :

1.  n =(-35-√-855)/52=(-35-3i√ 95 )/52= -0.6731-0.5623i
2.  n =(-35+√-855)/52=(-35+3i√ 95 )/52= -0.6731+0.5623i