5-2x2=-15 
Two solutions were found :
                   x = ± √10 = ± 3.1623
Rearrange:
Rearrange the equation by subtracting what is to the right of the equal sign from both sides of the equation :
                     5-2*x^2-(-15)=0 
Step by step solution :
Step  1  :
Equation at the end of step  1  :
  (5 -  2x2) -  -15  = 0 
Step  2  :
Step  3  :
Pulling out like terms :
 3.1     Pull out like factors :
   20 - 2x2  =   -2 • (x2 - 10) 
Trying to factor as a Difference of Squares :
 3.2      Factoring:  x2 - 10 
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 : 10 is not a square !!
Ruling : Binomial can not be factored as the difference of two perfect squares.
Equation at the end of step  3  :
  -2 • (x2 - 10)  = 0 
Step  4  :
Equations which are never true :
 4.1      Solve :    -2   =  0
This equation has no solution.
A a non-zero constant never equals zero.
Solving a Single Variable Equation :
 4.2      Solve  :    x2-10 = 0 
 Add  10  to both sides of the equation : 
                      x2 = 10
 
 When two things are equal, their square roots are equal. Taking the square root of the two sides of the equation we get:  
                      x  =  ± √ 10  
 The equation has two real solutions  
 These solutions are  x = ± √10 = ± 3.1623  
 
Two solutions were found :
                   x = ± √10 = ± 3.1623