Factor the expression. 10 ( z + 2 ) - z ( z + 2 )?

Find the common factor: (z + 2)

and you get:
(z + 2)(10 - z)

= (10 - z)(z + 2)

Answer: (z - 10)(z + 2) or (10 - z)(z + 2)

Proof:
10z + 20 - z² - 2z = 0
- z² + 8z + 20 = 0
z² - 8z = 20
z² - 4z = 20 + 4²
z² - 4z = 20 + 16
(z - 4)² = 36
z - 4 = 6

1st factor:
= z - 4 + 6
= z + 2

2nd factor:
= (- z² + 8z + 20)/(z + 2)
= - z + 10 or
= z - 10

(z + 2)(10 - z)

(z+2)(10-z)

(z+2)(10-z)

10z+20-z²-2z

-z²+8z+20

10(z + 2) - z(z + 2)
= (z + 2)(10 - z)

common factor : ( z + 2 )

you will have:

( z + 2 ) ( 10 - z )