Answer :

belcatya
if you noted 2-6+4=0  ⇒z₁=1 ⇒ one of factor is (z-1)
so 2z²-2z-4z+4=0
(2z²-2z)-(4z-4)=0
2z(z-1)-4(z-1)=0
(z-1)(2z-4)=0
2z-4=0
2z=4
z₂=2
Answer: z₁=1, z₂=2
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2z²-6z+4=0

Divide by 2 to everything 

z²-3z+2=0

Think of two numbers that multiply to get 2 and add to get -3 in order to factorise

These numbers are -2 and -1

(z-2)(z-1)=0

Therefore z= 2 and z= 1

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