\[ \left \{x'(t)=a x(t)+b y(t),y'(t)=b y(t)+c x(t)\right \} \] ✓ Mathematica : cpu = 0.0494356 (sec), leaf count = 362
\[\left \{\left \{x(t)\to \frac {e^{\frac {1}{2} t \left (-\sqrt {a^2-2 a b+b^2+4 b c}+a+b\right )} \left (a c_1 \left (e^{t \sqrt {a^2-2 a b+b^2+4 b c}}-1\right )+c_1 \sqrt {a^2-2 a b+b^2+4 b c} \left (e^{t \sqrt {a^2-2 a b+b^2+4 b c}}+1\right )-b \left (c_1-2 c_2\right ) \left (e^{t \sqrt {a^2-2 a b+b^2+4 b c}}-1\right )\right )}{2 \sqrt {a^2-2 a b+b (b+4 c)}},y(t)\to \frac {e^{\frac {1}{2} t \left (-\sqrt {a^2-2 a b+b^2+4 b c}+a+b\right )} \left (2 c c_1 \left (e^{t \sqrt {a^2-2 a b+b^2+4 b c}}-1\right )+c_2 \left (a \left (-e^{t \sqrt {a^2-2 a b+b^2+4 b c}}\right )+b \left (e^{t \sqrt {a^2-2 a b+b^2+4 b c}}-1\right )+\sqrt {a^2-2 a b+b^2+4 b c} \left (e^{t \sqrt {a^2-2 a b+b^2+4 b c}}+1\right )+a\right )\right )}{2 \sqrt {a^2-2 a b+b (b+4 c)}}\right \}\right \}\]
✓ Maple : cpu = 0.079 (sec), leaf count = 177
\[ \left \{ \left \{ x \left ( t \right ) ={\it \_C1}\,{{\rm e}^{{\frac {t}{2} \left ( a+b+\sqrt {{b}^{2}+ \left ( -2\,a+4\,c \right ) b+{a}^{2}} \right ) }}}+{\it \_C2}\,{{\rm e}^{{\frac {t}{2} \left ( a+b-\sqrt {{b}^{2}+ \left ( -2\,a+4\,c \right ) b+{a}^{2}} \right ) }}},y \left ( t \right ) ={\frac {1}{2\,b} \left ( -{\it \_C2}\, \left ( a-b+\sqrt {{b}^{2}+ \left ( -2\,a+4\,c \right ) b+{a}^{2}} \right ) {{\rm e}^{{\frac {t}{2} \left ( a+b-\sqrt {{b}^{2}+ \left ( -2\,a+4\,c \right ) b+{a}^{2}} \right ) }}}-{\it \_C1}\,{{\rm e}^{{\frac {t}{2} \left ( a+b+\sqrt {{b}^{2}+ \left ( -2\,a+4\,c \right ) b+{a}^{2}} \right ) }}} \left ( a-b-\sqrt {{b}^{2}+ \left ( -2\,a+4\,c \right ) b+{a}^{2}} \right ) \right ) } \right \} \right \} \]