Math F.2

1)
3x - y = 13..........(1)
2x + 3y = - 6..........(2)
(1) : x = (13 + y) / 3..........(3)
Subst. (3) into (2) :
2[(13 + y) / 3] + 3y = -6
(26 + 2y) / 3 + 3y = -6
(26 + 2y + 9y) = -18
11y = -44
y = -4..........(4)
Put (4) into (1)
3x - (-4) = 13
x = 3
2)
2x -5y = 2..........(1)
3x + 2y = 22..........(2)
(1) : x = (2 + 5y) / 2..........(3)
Subst (3) into (2) :
3(2 + 5y) / 2 + 2y = 22
(6 + 15y) / 2 + 2y = 22
6 + 15y + 4y = 44
19y = 38
y = 2..........(4)
Put (4) into (1).
2x - 10 = 2
x = 6
3) By the result of (2) , solve the simultaneous equations
2(a-b)-5(a+b)=2
3(a-b)+2(a+b)=22
a - b = x
a - b = 6..........(1)
a + b = y
a + b = 2..........(2)
(1) : a = 6 + b..........(3)
Subst. (3) into (2)
6 + 2b = 2
2b = -4
b = -2..........(3)
Put (3) into (1)
a - (-2) = 6
a = 4