Solution - Quadratic equations

Step by step solution :

Step  1  :

Equation at the end of step  1  :

  ((0 -  (22•3x2)) +  x) -  70  = 0 

Step  2  :

Step  3  :

Pulling out like terms :

 3.1     Pull out like factors :

   -12x² + x - 70  =   -1 • (12x² - x + 70) 

Trying to factor by splitting the middle term

 3.2     Factoring  12x² - x + 70 

The first term is,  12x²  its coefficient is  12 .
The middle term is,  -x  its coefficient is  -1 .
The last term, "the constant", is  +70 

Step-1 : Multiply the coefficient of the first term by the constant   12 • 70 = 840 

Step-2 : Find two factors of  840  whose sum equals the coefficient of the middle term, which is   -1 .

For tidiness, printing of 58 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  :

  -12x2 + x - 70  = 0 

Step  4  :

Parabola, Finding the Vertex :

 4.1      Find the Vertex of   y = -12x²+x-70

Parabolas have a highest or a lowest point called the Vertex .   Our parabola opens down and accordingly has a highest point (AKA absolute maximum) .    We know this even before plotting  "y"  because the coefficient of the first term, -12 , is negative (smaller 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   0.0417  

 Plugging into the parabola formula   0.0417  for  x  we can calculate the  y -coordinate : 
  y = -12.0 * 0.04 * 0.04 + 1.0 * 0.04 - 70.0
or   y = -69.979

Parabola, Graphing Vertex and X-Intercepts :

Root plot for :  y = -12x²+x-70
Axis of Symmetry (dashed)  {x}={ 0.04} 
Vertex at  {x,y} = { 0.04,-69.98} 
Function has no real roots

Solve Quadratic Equation by Completing The Square

 4.2     Solving   -12x²+x-70 = 0 by Completing The Square .

 Multiply both sides of the equation by  (-1)  to obtain positive coefficient for the first term:
 12x²-x+70 = 0  Divide both sides of the equation by  12  to have 1 as the coefficient of the first term :
   x²-(1/12)x+(35/6) = 0

Subtract  35/6  from both side of the equation :
   x²-(1/12)x = -35/6

Now the clever bit: Take the coefficient of  x , which is  1/12 , divide by two, giving  1/24 , and finally square it giving  1/576 

Add  1/576  to both sides of the equation :
  On the right hand side we have :
   -35/6  +  1/576   The common denominator of the two fractions is  576   Adding  (-3360/576)+(1/576)  gives  -3359/576 
  So adding to both sides we finally get :
   x²-(1/12)x+(1/576) = -3359/576

Adding  1/576  has completed the left hand side into a perfect square :
   x²-(1/12)x+(1/576)  =
   (x-(1/24)) • (x-(1/24))  =
  (x-(1/24))²
Things which are equal to the same thing are also equal to one another. Since
   x²-(1/12)x+(1/576) = -3359/576 and
   x²-(1/12)x+(1/576) = (x-(1/24))²
then, according to the law of transitivity,
   (x-(1/24))² = -3359/576

We'll refer to this Equation as  Eq. #4.2.1  

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

Note that the square root of
   (x-(1/24))²   is
   (x-(1/24))^2/2 =
  (x-(1/24))¹ =
   x-(1/24)

Now, applying the Square Root Principle to  Eq. #4.2.1  we get:
   x-(1/24) = √ -3359/576

Add  1/24  to both sides to obtain:
   x = 1/24 + √ -3359/576
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
   x² - (1/12)x + (35/6) = 0
   has two solutions:
  x = 1/24 + √ 3359/576 •  i 
   or
  x = 1/24 - √ 3359/576 •  i 

Note that  √ 3359/576 can be written as
  √ 3359  / √ 576   which is √ 3359  / 24

Solve Quadratic Equation using the Quadratic Formula

 4.3     Solving    -12x²+x-70 = 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   =    -12
                      B   =    1
                      C   =  -70

Accordingly,  B²  -  4AC   =
                     1 - 3360 =
                     -3359

Applying the quadratic formula :

               -1 ± √ -3359
   x  =    ———————
                        -24

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,√ -3359  = 
                    √ 3359 • (-1)  =
                    √ 3359  • √ -1   =
                    ±  √ 3359  • i

  √ 3359   , rounded to 4 decimal digits, is  57.9569
 So now we are looking at:
           x  =  ( -1 ±  57.957 i ) / -24

Two imaginary solutions :

 x =(-1+√-3359)/-24=(1-i√ 3359 )/24= 0.0417+2.4149i
  or: 
 x =(-1-√-3359)/-24=(1+i√ 3359 )/24= 0.0417-2.4149i

Two solutions were found :

1.  x =(-1-√-3359)/-24=(1+i√ 3359 )/24= 0.0417-2.4149i
2.  x =(-1+√-3359)/-24=(1-i√ 3359 )/24= 0.0417+2.4149i