Question

x elevado a2 -28x+160=0

Answer 1

Δ = 784 - 640
Δ = 144

x = 28+ -√144/2
x = 28 +-12/2

x' = 28 + 12/2
x' = 40/2 = 20

x''= 28 -12/2
x'' = 16/2 = 8           ok

Answer 2

x²-28x+160=0

a= 1 b= -28 c=160

Δ= b² - 4.a.c
Δ= (-28)² - 4.1.160
Δ= 784 - 640
Δ= 144

x=( -b +/- √Δ)/2.a
x= (28 +/- √144)/2.1
x= (28 +/- 12)/2

x'= (28 + 12)/2 
x'= 40/2
x'= 20

x"= (28 - 12)/2
x"= 16/2
x"=8 

Espero ter ajudado.