Question

I need help

Answer 1

2:

7a-b+4c=0

=>14a-2b+8c=0

=>2b=14a+8c

P(2)=4a+2b+c=4a+c+14a+8c=18a+9c

P(-1)=a-b+c=a+c-7a-4c=-6a-3c

P(2)*P(-1)

=(18a+9c)(-6a-3c)

=-3(2a+c)*9*(2a+c)

=-27(2a+c)^2<=0(luôn đúng)