Ответ:

1)

3x+4y=7 --> 3x = 7 - 4y

9x-4y= -7 --> 9x-4y= -7 --> 3( 7-4y) - 4y = -7

21-12y-4y=-7

21-16y=-7

-16y=-21-7

-16y=-28

y= 1,75

3x+4×1,75=7. 9x-4×1,75=-7

3x+7=7. 9x-7=-7

3x=0. 9x=0

x=0. x=0.

(0;1,75)

2)

x-3y=6. --> x= 6+3y

2y-5x=-4-->2y-5×(6+3y)=-4

2y-30-15y=-4

-13y=-4+30

-13y=26

y=-2

x-3×(-2)=6. 2×(-2)-5x=-4

x+6=6: -4-5x=-4

x=0. -5x=0

x=0. (0;-2)