Solution - Nonlinear equations

Step by step solution :

Step  1  :

Trying to factor as a Difference of Squares :

 1.1      Factoring:  x²-84 

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 : 84 is not a square !!

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

Equation at the end of step  1  :

  x2 - 84  = 0 

Step  2  :

Solving a Single Variable Equation :

 2.1      Solve  :    x²-84 = 0 

 Add  84  to both sides of the equation : 
                      x² = 84
 
 When two things are equal, their square roots are equal. Taking the square root of the two sides of the equation we get:  
                      x  =  ± √ 84  

 Can  √ 84 be simplified ?

Yes!   The prime factorization of  84   is
   2•2•3•7 
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).

√ 84   =  √ 2•2•3•7   =
                ±  2 • √ 21

The equation has two real solutions  
 These solutions are  x = 2 • ± √21 = ± 9.1652  
 

Two solutions were found :