For quadratics of the form

ax² + bx + c = 0

the solutions are of the form

x = (-b +/- √(b² - 4ac)) / 2a

With a = 1, b = -4 and c = 20, this gives

x = (4 +/- √(16 - 80)) / 2

= (4 +/- √(-64)) / 2

= (4 +/- 8i)/2

ie the solutions are

x = 2 + 4i and 2 - 2i

Isolate the x terms:

x^2 - 4x = -20

Complete the square by adding 4 to both sides and factoring out the left-hand side:

(x - 2)^2 = -16

Square root both sides:

x - 2 = ± 4i

Add 2 to both sides:

x = 2 ± 4i

x²-4x+20=0

x=[4±√(16-80)]/2

x=2±4i

x = 10

Use the formula (-b±√(b^2-4ac))/2a for ax^2+bx+c = 0

we get, x = [ -(-4)±√{(-4)^2-4.1.20} ] / 2 = {4±(16-80)}/2 = (4±√-64)/2 = (4±8i)/2 = 2±4i

The two answers are 2+4i and 2-4i

2x – 4x + 20 = 0

–2x = –20

x = 10