lazinhojose A)
x²-5x+6=0

x+x'=-b/a
x.x'=c/a

x+x'=-(-5)/1
x+x'=5
x.x'=6/1
x.x'=6

b)
5x²-8x+4=0

x+x'=-(-8)/5
x+x'=8/5
x+x'=1,6

x.x'=4/5
x.x'=0,8