48.
\(S_{ABC}=\dfrac{1}{2}\left|\left(x_B-x_A\right)\left(y_C-y_A\right)-\left(x_C-x_A\right)\left(y_B-y_A\right)\right|\)
\(=\dfrac{1}{2}\left|\left(-1\right).0-\left(-2\right).3\right|=3\)
Đáp án D
49.
\(\Rightarrow\left(m^2+1\right)x-1=x+1\)
\(\Rightarrow m^2x+x=x+2\)
\(\Rightarrow m^2x=2\)
\(\Rightarrow x=\dfrac{2}{m^2}\)
Đáp án D