Question

Bài3: xác định a, b để đồ thị hs y = ax + b đi qua 2 điểm A và B trong các trường hợp sau: a) A(4; 3), B(-6;-7). b) A(3;-1), B(-3;-2) c) A(2; 1), B(1; 2) d) A(1; 3), B(3; 2).

Answer 1

Lời giải:

a)

\(\left\{\begin{matrix} y_A=ax_A+b\\ y_B=ax_B+b\end{matrix}\right.\Leftrightarrow \left\{\begin{matrix} 3=4a+b\\ -7=-6a+b\end{matrix}\right.\Leftrightarrow \left\{\begin{matrix} a=1\\ b=-1\end{matrix}\right.\)

b)

\(\left\{\begin{matrix} y_A=ax_A+b\\ y_B=ax_B+b\end{matrix}\right.\Leftrightarrow \left\{\begin{matrix} -1=3a+b\\ -2=-3a+b\end{matrix}\right.\Rightarrow \left\{\begin{matrix} a=\frac{1}{6}\\ b=\frac{-3}{2}\end{matrix}\right.\)

c)

\(\left\{\begin{matrix} y_A=ax_A+b\\ y_B=ax_B+b\end{matrix}\right.\Leftrightarrow \left\{\begin{matrix} 1=2a+b\\ 2=a+b\end{matrix}\right.\Rightarrow \left\{\begin{matrix} a=-1\\ b=3\end{matrix}\right.\)

d)

\(\left\{\begin{matrix} y_A=ax_A+b\\ y_B=ax_B+b\end{matrix}\right.\Leftrightarrow \left\{\begin{matrix} 3=a+b\\ 2=3a+b\end{matrix}\right.\Rightarrow \left\{\begin{matrix} a=\frac{-1}{2}\\ b=\frac{7}{2}\end{matrix}\right.\)