Let's solve your equation step by step.
(x-5)^2 -4(x - 5) - 21 = 0
Step 1: Simply both sides of the equation.
x^2 - 14x + 24=0
Step 2: Factor left side of the equation.
(x - 2)(x - 12) = 0
Step 3: Set factors equal to 0.
x - 2 = 0 or x - 12 = 0
x = 2 or x = 12
Answer:
x = 2 or x = 12