Solution - Quadratic equations

Reformatting the input :

Changes made to your input should not affect the solution:

(1): "87.5" was replaced by "(875/10)".

Rearrange:

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

                     -(875/10)+20*x-(x^2)=0 

Step by step solution :

Step  1  :

            175
 Simplify   ———
             2 

Equation at the end of step  1  :

         175             
  ((0 -  ———) +  20x) -  x2  = 0 
          2              

Step  2  :

Rewriting the whole as an Equivalent Fraction :

 2.1   Adding a whole to a fraction

Rewrite the whole as a fraction using  2  as the denominator :

           20x     20x • 2
    20x =  ———  =  ———————
            1         2   

Equivalent fraction : The fraction thus generated looks different but has the same value as the whole

Common denominator : The equivalent fraction and the other fraction involved in the calculation share the same denominator

Adding fractions that have a common denominator :

 2.2       Adding up the two equivalent fractions
Add the two equivalent fractions which now have a common denominator

Combine the numerators together, put the sum or difference over the common denominator then reduce to lowest terms if possible:

 -175 + 20x • 2     40x - 175
 ——————————————  =  —————————
       2                2    

Equation at the end of step  2  :

  (40x - 175)    
  ——————————— -  x2  = 0 
       2         

Step  3  :

Rewriting the whole as an Equivalent Fraction :

 3.1   Subtracting a whole from a fraction

Rewrite the whole as a fraction using  2  as the denominator :

          x2     x2 • 2
    x2 =  ——  =  ——————
          1        2   

Step  4  :

Pulling out like terms :

 4.1     Pull out like factors :

   40x - 175  =   5 • (8x - 35) 

Adding fractions that have a common denominator :

 4.2       Adding up the two equivalent fractions

 5 • (8x-35) - (x2 • 2)     -2x2 + 40x - 175
 ——————————————————————  =  ————————————————
           2                       2        

Step  5  :

Pulling out like terms :

 5.1     Pull out like factors :

   -2x² + 40x - 175  =   -1 • (2x² - 40x + 175) 

Trying to factor by splitting the middle term

 5.2     Factoring  2x² - 40x + 175 

The first term is,  2x²  its coefficient is  2 .
The middle term is,  -40x  its coefficient is  -40 .
The last term, "the constant", is  +175 

Step-1 : Multiply the coefficient of the first term by the constant   2 • 175 = 350 

Step-2 : Find two factors of  350  whose sum equals the coefficient of the middle term, which is   -40 .

For tidiness, printing of 18 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  5  :

  -2x2 + 40x - 175
  ————————————————  = 0 
         2        

Step  6  :

When a fraction equals zero :

 6.1    When a fraction equals zero ...

Where a fraction equals zero, its numerator, the part which is above the fraction line, must equal zero.

Now,to get rid of the denominator, Tiger multiplys both sides of the equation by the denominator.

Here's how:

  -2x2+40x-175
  ———————————— • 2 = 0 • 2
       2      

Now, on the left hand side, the  2  cancels out the denominator, while, on the right hand side, zero times anything is still zero.

The equation now takes the shape :
   -2x²+40x-175  = 0

Parabola, Finding the Vertex :

 6.2      Find the Vertex of   y = -2x²+40x-175

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, -2 , 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  10.0000  

 Plugging into the parabola formula  10.0000  for  x  we can calculate the  y -coordinate : 
  y = -2.0 * 10.00 * 10.00 + 40.0 * 10.00 - 175.0
or   y = 25.000

Parabola, Graphing Vertex and X-Intercepts :

Root plot for :  y = -2x²+40x-175
Axis of Symmetry (dashed)  {x}={10.00} 
Vertex at  {x,y} = {10.00,25.00} 
 x -Intercepts (Roots) :
Root 1 at  {x,y} = {13.54, 0.00} 
Root 2 at  {x,y} = { 6.46, 0.00} 

Solve Quadratic Equation by Completing The Square

 6.3     Solving   -2x²+40x-175 = 0 by Completing The Square .

 Multiply both sides of the equation by  (-1)  to obtain positive coefficient for the first term:
 2x²-40x+175 = 0  Divide both sides of the equation by  2  to have 1 as the coefficient of the first term :
   x²-20x+(175/2) = 0

Subtract  175/2  from both side of the equation :
   x²-20x = -175/2

Now the clever bit: Take the coefficient of  x , which is  20 , divide by two, giving  10 , and finally square it giving  100 

Add  100  to both sides of the equation :
  On the right hand side we have :
   -175/2  +  100    or,  (-175/2)+(100/1) 
  The common denominator of the two fractions is  2   Adding  (-175/2)+(200/2)  gives  25/2 
  So adding to both sides we finally get :
   x²-20x+100 = 25/2

Adding  100  has completed the left hand side into a perfect square :
   x²-20x+100  =
   (x-10) • (x-10)  =
  (x-10)²
Things which are equal to the same thing are also equal to one another. Since
   x²-20x+100 = 25/2 and
   x²-20x+100 = (x-10)²
then, according to the law of transitivity,
   (x-10)² = 25/2

We'll refer to this Equation as  Eq. #6.3.1  

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

Note that the square root of
   (x-10)²   is
   (x-10)^2/2 =
  (x-10)¹ =
   x-10

Now, applying the Square Root Principle to  Eq. #6.3.1  we get:
   x-10 = √ 25/2

Add  10  to both sides to obtain:
   x = 10 + √ 25/2

Since a square root has two values, one positive and the other negative
   x² - 20x + (175/2) = 0
   has two solutions:
  x = 10 + √ 25/2
   or
  x = 10 - √ 25/2

Note that  √ 25/2 can be written as
  √ 25  / √ 2   which is 5 / √ 2 

It is customary to further simplify until the denominator is radical free.

This can be achieved here by multiplying both the nominator and the denominator by  √ 2 

Following this multiplication, the numeric value of   5 /√ 2 remains unchanged, as it is multiplyed by  √ 2  / √ 2  which equals   1 

   OK, let's do it:

  5 •  √ 2       5 •  √ 2 
—————————————— = —————————————
√ 2  • √ 2          2

Solve Quadratic Equation using the Quadratic Formula

 6.4     Solving    -2x²+40x-175 = 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   =     -2
                      B   =    40
                      C   =  -175

Accordingly,  B²  -  4AC   =
                     1600 - 1400 =
                     200

Applying the quadratic formula :

               -40 ± √ 200
   x  =    ——————
                      -4

Can  √ 200 be simplified ?

Yes!   The prime factorization of  200   is
   2•2•2•5•5 
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).

√ 200   =  √ 2•2•2•5•5   =2•5•√ 2   =
                ±  10 • √ 2

  √ 2   , rounded to 4 decimal digits, is   1.4142
 So now we are looking at:
           x  =  ( -40 ± 10 •  1.414 ) / -4

Two real solutions:

 x =(-40+√200)/-4=10-5/2√ 2 = 6.464

or:

 x =(-40-√200)/-4=10+5/2√ 2 = 13.536

Two solutions were found :

1.  x =(-40-√200)/-4=10+5/2√ 2 = 13.536
2.  x =(-40+√200)/-4=10-5/2√ 2 = 6.464