phuong tring duong thang di qua 2 diem la do thi co dang y=ax+b
a,\(A\left(1;5\right)\in\) do thi nen ta co \(5=a+b\)
\(B\left(-2;-1\right)\) nen ta co \(-1=-2a+b\)
giai he pt ta co a=2, b=3 nen do thi co dang \(y=2x+3\)
b tuong tu ta co he \(\hept{\begin{cases}1=a+b\\-3=5a+b\end{cases}\Rightarrow a=-1,b=2}\)
do thi co dang \(y=-x+2\)