What are the roots of the equation x^2+4x-16=0

OK so you need to use the quadratic formula with a=1, b=4, c=-16.
   
     −b±√b^2−4ac
x=    
            2a   

      −(4)±√(4)^2−4(1)(−16)
x=
                 2(1)    
      
         −4±√80
x=
            2

Your final answer is:  x=−2+2√5 or x=−2−2√5

X² + 4x - 16 = 0
x = -(4) ± √((4)² - 4(1)(-16))
                     2(1)
x = -4 ± √(16 + 64)
                 2
x = -4 ± √(80)
             2
x = -4 ± 4√(5)
             2
x = -2 ± 2√(5)
x = -2 + 2√(5)    U    x = -2 - 2√(5)

The answer to that is 6