Solution - Equations reducible to quadratic form

Step by step solution :

Step  1  :

Equation at the end of step  1  :

  ((5 • (x4)) -  (2•3x2)) -  8  = 0 
 Step  2  :

Equation at the end of step  2  :

  (5x4 -  (2•3x2)) -  8  = 0 

Step  3  :

Trying to factor by splitting the middle term

 3.1     Factoring  5x⁴-6x²-8 

The first term is,  5x⁴  its coefficient is  5 .
The middle term is,  -6x²  its coefficient is  -6 .
The last term, "the constant", is  -8 

Step-1 : Multiply the coefficient of the first term by the constant   5 • -8 = -40 

Step-2 : Find two factors of  -40  whose sum equals the coefficient of the middle term, which is   -6 .

Step-3 : Rewrite the polynomial splitting the middle term using the two factors found in step 2 above,  -10  and  4 
                     5x⁴ - 10x² + 4x² - 8

Step-4 : Add up the first 2 terms, pulling out like factors :
                    5x² • (x²-2)
              Add up the last 2 terms, pulling out common factors :
                    4 • (x²-2)
Step-5 : Add up the four terms of step 4 :
                    (5x²+4)  •  (x²-2)
             Which is the desired factorization

Trying to factor as a Difference of Squares :

 3.2      Factoring:  x²-2 

Theory : A difference of two perfect squares,  A² - B²  can be factored into  (A+B) • (A-B)

Proof :  (A+B) • (A-B) =
         A² - AB + BA - B² =
         A² - AB + AB - B² =
         A² - B²

Note :  AB = BA is the commutative property of multiplication.

Note :  - AB + AB equals zero and is therefore eliminated from the expression.

Check : 2 is not a square !!

Ruling : Binomial can not be factored as the difference of two perfect squares.

Polynomial Roots Calculator :

 3.3    Find roots (zeroes) of :       F(x) = 5x²+4
Polynomial Roots Calculator is a set of methods aimed at finding values of  x  for which   F(x)=0  

Rational Roots Test is one of the above mentioned tools. It would only find Rational Roots that is numbers  x  which can be expressed as the quotient of two integers

The Rational Root Theorem states that if a polynomial zeroes for a rational number  P/Q   then  P  is a factor of the Trailing Constant and  Q  is a factor of the Leading Coefficient

In this case, the Leading Coefficient is  5  and the Trailing Constant is  4.

 The factor(s) are:

of the Leading Coefficient :  1,5
 of the Trailing Constant :  1 ,2 ,4

 Let us test ....

Polynomial Roots Calculator found no rational roots

Equation at the end of step  3  :

  (x2 - 2) • (5x2 + 4)  = 0 

Step  4  :

Theory - Roots of a product :

 4.1    A product of several terms equals zero. 

 When a product of two or more terms equals zero, then at least one of the terms must be zero. 

 We shall now solve each term = 0 separately 

 In other words, we are going to solve as many equations as there are terms in the product 

 Any solution of term = 0 solves product = 0 as well.

Solving a Single Variable Equation :

 4.2      Solve  :    x²-2 = 0 

 Add  2  to both sides of the equation : 
                      x² = 2
 
 When two things are equal, their square roots are equal. Taking the square root of the two sides of the equation we get:  
                      x  =  ± √ 2  

 The equation has two real solutions  
 These solutions are  x = ± √2 = ± 1.4142  
 

Solving a Single Variable Equation :

 4.3      Solve  :    5x²+4 = 0 

 Subtract  4  from both sides of the equation : 
                      5x² = -4
Divide both sides of the equation by 5:
                     x² = -4/5 = -0.800
 
 When two things are equal, their square roots are equal. Taking the square root of the two sides of the equation we get:  
                      x  =  ± √ -4/5  

 In Math,  i  is called the imaginary unit. It satisfies   i²  =-1. Both   i   and   -i   are the square roots of   -1 

Accordingly,  √ -4/5  =
                    √ -1• 4/5   =
                    √ -1 •√  4/5   =
                    i •  √ 4/5

The equation has no real solutions. It has 2 imaginary, or complex solutions.

                      x=  0.0000 + 0.8944 i 
                      x=  0.0000 - 0.8944 i 

Supplement : Solving Quadratic Equation Directly

Solving    5x4-6x2-8  = 0   directly 

Earlier we factored this polynomial by splitting the middle term. let us now solve the equation by Completing The Square and by using the Quadratic Formula

Solving a Single Variable Equation :

Equations which are reducible to quadratic :

 5.1     Solve   5x⁴-6x²-8 = 0

This equation is reducible to quadratic. What this means is that using a new variable, we can rewrite this equation as a quadratic equation Using  w , such that  w = x²  transforms the equation into :
 5w²-6w-8 = 0

Solving this new equation using the quadratic formula we get two real solutions :
   2.0000  or  -0.8000

Now that we know the value(s) of  w , we can calculate  x  since  x  is  √ w  

Doing just this we discover that the solutions of
   5x⁴-6x²-8 = 0
  are either : 
  x =√ 2.000 = 1.41421  or :
  x =√ 2.000 = -1.41421  or :
  x =√-0.800 = 0.0 + 0.89443 i  or :
  x =√-0.800 = 0.0 - 0.89443 i

Four solutions were found :

1.   x=  0.0000 - 0.8944 i 
   
2.   x=  0.0000 + 0.8944 i 
   
3.  x = ± √2 = ± 1.4142