First one:
Take square root of both sides of the equation to get
x^2 - 82 = = 18 or -18
x^2 = 100 or 64
x= + or - 10 or + - 8 -10,-8,8,10
Second one
x^2+6x-16=0 factor
(x-2)(x+8) = 0 so x = 2 or -8 -8 is the smallest
Third one
(x+6)^2 = -25
x+6 = -5i 5i
x = -6-5i -6+5i