Solution - Quadratic equations

Step by step solution :

Step  1  :

Equation at the end of step  1  :

  (11x2 +  121x) +  218  = 0 

Step  2  :

Trying to factor by splitting the middle term

 2.1     Factoring  11x²+121x+218 

The first term is,  11x²  its coefficient is  11 .
The middle term is,  +121x  its coefficient is  121 .
The last term, "the constant", is  +218 

Step-1 : Multiply the coefficient of the first term by the constant   11 • 218 = 2398 

Step-2 : Find two factors of  2398  whose sum equals the coefficient of the middle term, which is   121 .

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

Equation at the end of step  2  :

  11x2 + 121x + 218  = 0 

Step  3  :

Parabola, Finding the Vertex :

 3.1      Find the Vertex of   y = 11x²+121x+218

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, 11 , 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  -5.5000  

 Plugging into the parabola formula  -5.5000  for  x  we can calculate the  y -coordinate : 
  y = 11.0 * -5.50 * -5.50 + 121.0 * -5.50 + 218.0
or   y = -114.750

Parabola, Graphing Vertex and X-Intercepts :

Root plot for :  y = 11x²+121x+218
Axis of Symmetry (dashed)  {x}={-5.50} 
Vertex at  {x,y} = {-5.50,-114.75} 
 x -Intercepts (Roots) :
Root 1 at  {x,y} = {-8.73, 0.00} 
Root 2 at  {x,y} = {-2.27, 0.00} 

Solve Quadratic Equation by Completing The Square

 3.2     Solving   11x²+121x+218 = 0 by Completing The Square .

 Divide both sides of the equation by  11  to have 1 as the coefficient of the first term :
   x²+11x+(218/11) = 0

Subtract  218/11  from both side of the equation :
   x²+11x = -218/11

Now the clever bit: Take the coefficient of  x , which is  11 , divide by two, giving  11/2 , and finally square it giving  121/4 

Add  121/4  to both sides of the equation :
  On the right hand side we have :
   -218/11  +  121/4   The common denominator of the two fractions is  44   Adding  (-872/44)+(1331/44)  gives  459/44 
  So adding to both sides we finally get :
   x²+11x+(121/4) = 459/44

Adding  121/4  has completed the left hand side into a perfect square :
   x²+11x+(121/4)  =
   (x+(11/2)) • (x+(11/2))  =
  (x+(11/2))²
Things which are equal to the same thing are also equal to one another. Since
   x²+11x+(121/4) = 459/44 and
   x²+11x+(121/4) = (x+(11/2))²
then, according to the law of transitivity,
   (x+(11/2))² = 459/44

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
   (x+(11/2))²   is
   (x+(11/2))^2/2 =
  (x+(11/2))¹ =
   x+(11/2)

Now, applying the Square Root Principle to  Eq. #3.2.1  we get:
   x+(11/2) = √ 459/44

Subtract  11/2  from both sides to obtain:
   x = -11/2 + √ 459/44

Since a square root has two values, one positive and the other negative
   x² + 11x + (218/11) = 0
   has two solutions:
  x = -11/2 + √ 459/44
   or
  x = -11/2 - √ 459/44

Note that  √ 459/44 can be written as
  √ 459  / √ 44 

Solve Quadratic Equation using the Quadratic Formula

 3.3     Solving    11x²+121x+218 = 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   =     11
                      B   =   121
                      C   =  218

Accordingly,  B²  -  4AC   =
                     14641 - 9592 =
                     5049

Applying the quadratic formula :

               -121 ± √ 5049
   x  =    ————————
                        22

Can  √ 5049 be simplified ?

Yes!   The prime factorization of  5049   is
   3•3•3•11•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).

√ 5049   =  √ 3•3•3•11•17   =
                ±  3 • √ 561

  √ 561   , rounded to 4 decimal digits, is  23.6854
 So now we are looking at:
           x  =  ( -121 ± 3 •  23.685 ) / 22

Two real solutions:

 x =(-121+√5049)/22=-11/2+3/22√ 561 = -2.270

or:

 x =(-121-√5049)/22=-11/2-3/22√ 561 = -8.730

Two solutions were found :

1.  x =(-121-√5049)/22=-11/2-3/22√ 561 = -8.730
2.  x =(-121+√5049)/22=-11/2+3/22√ 561 = -2.270