Пояснення:

в)

[tex]\displaystyle\\\left \{ {{1,2m-3n=0\ |:3} \atop {2m+1,5n=-13\ |*2}} \right.\ \ \ \ \left \{ {{0,4m-n=0} \atop {2m+1,5n=-13}} \right. \ \ \ \ \left \{ {{n=0,4m} \atop {2m+1,5*0,4m=-13}} \right. \\\\\\\left \{ {{n=0,4m} \atop {2m+0,6m=-13}} \right. \ \ \ \ \left \{ {{n=0,4m} \atop {2,6m=-13\ |:2,6}} \right. \ \ \ \ \left \{ {{n=0,4*(-5)} \atop {m=-5}} \right. \ \ \ \ \left \{ {{n=-2} \atop {m=-5}} \right. .[/tex]

Відповідь: m=-5,  n=-2.

г)

[tex]\displaystyle\\\left \{ {{\frac{1}{2}a+\frac{1}{3} b=\frac{1}{6}\ |*6 } \atop {\frac{1}{4}a -\frac{1}{2}b =\frac{3}{4} }\ |*4} \right. \ \ \ \ \left \{ {{3*a+2*b=1} \atop {1*a-2*b=3}} \right.\ \ \ \ \ \ +\left \{ {{3a+2b=1} \atop {a-2b=3}} \right. \\\\4a=4\ |:4\\\\a=1.\\\\3*1 +2b=1\\\\3+2b=1\\\\2b=-2\ |:2\\\\b=-1.[/tex]

Відповідь: a=1,  b=-1.