\[ \boxed { {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) - \left ( Ay \left ( x \right ) -a \right ) \left ( By \left ( x \right ) -b \right ) =0} \]
Mathematica: cpu = 0.076010 (sec), leaf count = 68 \[ \left \{\left \{y(x)\to \frac {a e^{A b c_1+A b x}-b e^{a B c_1+a B x}}{A e^{A b c_1+A b x}-B e^{a B c_1+a B x}}\right \}\right \} \]
Maple: cpu = 0.047 (sec), leaf count = 59 \[ \left \{ y \left ( x \right ) ={\frac {{{\rm e}^{A{\it \_C1}\,b+Abx-B{ \it \_C1}\,a-Bax}}a-b}{A{{\rm e}^{A{\it \_C1}\,b+Abx-B{\it \_C1}\,a-Ba x}}-B}} \right \} \]
Sage: cpu = 0.152 (sec), leaf count = 0 \[ \left [\frac {\log \left (A y\left (x\right ) - a\right ) - \log \left (B y\left (x\right ) - b\right )}{B a - A b} = c + x, \text {\texttt {separable}}\right ] \]