`a)`

`{(2x-3y=2),(-5x+2y=3):}`

`{(4x-6y=4),(-15x+6y=9):}`

`{(-11x=13),(-15x+6y=9):}`

`{(x=-13/11),(-15·(-13/11)+6y=9):}`

`{(x=-13/11),(195/11+6y=9):}`

`{(x=-13/11),(6y=-96/11):}`

`{(x=-13/11),(y=-16/11):}`

Vậy `(x;y)=(-13/11;-16/11)`

`b)`

`{(x-2\sqrt{2}y=\sqrt{5}),(\sqrt{2}x+y=1-\sqrt{10}):}`

`{(\sqrt{2}x-4y=\sqrt{10}),(\sqrt{2}x+y=1-\sqrt{10}):}`

`{(-5y=\sqrt{10}-1+\sqrt{10}),(\sqrt{2}x+y=1-\sqrt{10}):}`

`{(-5y=2\sqrt{10}-1),(\sqrt{2}x+y=1-\sqrt{10}):}`

`{(y=(1-2\sqrt{10})/5),(\sqrt{2}x+(1-2\sqrt{10})/5=1-\sqrt{10}):}`

`{(y=(1-2\sqrt{10})/5),(\sqrt{2}x=1-\sqrt{10}-(1-2\sqrt{10})/5):}`

`{(y=(1-2\sqrt{10})/5),(\sqrt{2}x=(5-5\sqrt{10}-1+2\sqrt{10})/5):}`

`{(y=(1-2\sqrt{10})/5),(\sqrt{2}x=(4-3\sqrt{10})/5):}`

`{(y=(1-2\sqrt{10})/5),(x=(4-3\sqrt{10})/5·1/(\sqrt{2})):}`

`{(y=(1-2\sqrt{10})/5),(x=(4-3\sqrt{10})/(5\sqrt{2})):}`

`{(y=(1-2\sqrt{10})/5),(x=(\sqrt{2}(4-3\sqrt{10}))/(5\sqrt{2}·\sqrt{2})):}`

`{(y=(1-2\sqrt{10})/5),(x=(4\sqrt{2}-3\sqrt{20})/10):}`

`{(y=(1-2\sqrt{10})/5),(x=(4\sqrt{2}-6\sqrt{5})/10):}`

`{(y=(1-2\sqrt{10})/5),(x=(2(2\sqrt{2}-3\sqrt{5}))/10):}`

`{(y=(1-2\sqrt{10})/5),(x=(2\sqrt{2}-3\sqrt{5})/5):}`

Vậy `(x;y)=((2\sqrt{2}-3\sqrt{5})/5;(1-2\sqrt{10})/5)`

`c)`

`{((1+\sqrt{2})x+(1-\sqrt{2})y=5),((1+\sqrt{2})x+(1+\sqrt{2})y=3):}`

`{((1-\sqrt{2}-1-\sqrt{2})y=2),((1+\sqrt{2})x+(1+\sqrt{2})y=3):}`

`{(-2\sqrt{2}y=2),((1+\sqrt{2})x+(1+\sqrt{2})y=3):}`

`{(y=-1/(\sqrt{2})),((1+\sqrt{2})x+(1+\sqrt{2})y=3):}`

`{(y=-(\sqrt{2})/2),((1+\sqrt{2})x+(1+\sqrt{2})·(-(\sqrt{2})/2)=3):}`

`{(y=-(\sqrt{2})/2),((1+\sqrt{2})x-(\sqrt{2}(1+\sqrt{2}))/2=3):}`

`{(y=-(\sqrt{2})/2),((1+\sqrt{2})x-(\sqrt{2}+2)/2=3):}`

`{(y=-(\sqrt{2})/2),((1+\sqrt{2})x=3+(\sqrt{2}+2)/2):}`

`{(y=-(\sqrt{2})/2),((1+\sqrt{2})x=(6+\sqrt{2}+2)/2):}`

`{(y=-(\sqrt{2})/2),((1+\sqrt{2})x=(8+\sqrt{2})/2):}`

`{(y=-(\sqrt{2})/2),(x=(8+\sqrt{2})/2·1/(1+\sqrt{2})):}`

`{(y=-(\sqrt{2})/2),(x=(8+\sqrt{2})/(2(1+\sqrt{2}))):}`

`{(y=-(\sqrt{2})/2),(x=(8+\sqrt{2})/(2+2\sqrt{2})):}`

`{(y=-(\sqrt{2})/2),(x=((8+\sqrt{2})(2-2\sqrt{2}))/((2+2\sqrt{2})(2-2\sqrt{2}))):}`

`{(y=-(\sqrt{2})/2),(x=(16-16\sqrt{2}+2\sqrt{2}-8)/(4-8)):}`

`{(y=-(\sqrt{2})/2),(x=-(8-14\sqrt{2})/4):}`

`{(y=-(\sqrt{2})/2),(x=-(2(6-7\sqrt{2}))/4):}`

`{(y=-(\sqrt{2})/2),(x=-(6-7\sqrt{2})/2):}`

Vậy `(x;y)=(-(6-7\sqrt{2})/2;-(\sqrt{2})/2)`