Question

Answer 1

ta có 

\(P\left(\dfrac{-4}{5}\right)=\dfrac{-4}{5}a+b=0\left(1\right)\)

\(P\left(0\right)=a.0+b=4\Rightarrow b=4\)

 thay b=4 vào 1 ta đc

\(P\left(\dfrac{-4}{5}\right)=\dfrac{-4}{5}a+4=0\)

\(=>\dfrac{-4}{5}a=-4\)

\(=>a=-\dfrac{16}{5}\)

Answer 2

\(P\left(0\right)=4=>a.0+b=4\)

=>b=4

\(x=-\dfrac{4}{5}\)là nghiệm 

=>\(a.-\dfrac{4}{5}+4=0\)

\(=>a=5\)