Solution - Factoring binomials using the difference of squares

Rearrange:

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

                     0-(y^2-90)=0 

Step by step solution :

Step  1  :

Trying to factor as a Difference of Squares :

 1.1      Factoring:  90-y² 

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 :  90  is not a square !!

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

Equation at the end of step  1  :

  90 - y2  = 0 

Step  2  :

Solving a Single Variable Equation :

 2.1      Solve  :    -y²+90 = 0 

 Subtract  90  from both sides of the equation : 
                      -y² = -90
Multiply both sides of the equation by (-1) :  y² = 90


 
 When two things are equal, their square roots are equal. Taking the square root of the two sides of the equation we get:  
                      y  =  ± √ 90  

 Can  √ 90 be simplified ?

Yes!   The prime factorization of  90   is
   2•3•3•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).

√ 90   =  √ 2•3•3•5   =
                ±  3 • √ 10

The equation has two real solutions  
 These solutions are  y = 3 • ± √10 = ± 9.4868  
 

Two solutions were found :