7. (p+3)/4 - (q-2)/6 = 1 |×12
(p-1)/8 + (q+1)/6 = 2 |×24
3(p+3) - 2(q-2) = 12
3(p-1) + 4(q+1) = 48
3p+9-2q+4 = 12
3p-3+4q+4 = 48
3p-2q = 12-4-9 = -1
3p+4q = 48-4+3 = 47
Вычтем из уравнения 1 уравнение 2
-6q = -48
3p-2q = -1
q = 8
p = (-1+16)/3 = 5
Ответ: (5;8)
8. (7х-1)/4 - (2х+3)/3 = (3х-5у)/2 |×12
(5х-3у)/3 + (х+5у)/2 = 3х-у |×6
3(7х-1) - 4(2х+3) = 6(3х-5у)
2(5х-3у) + 3(х+5у) = 6(3х-у)
21х-3-8х-12 = 18х-30у
10х-6у+3х+15у = 18х-6у
21х-8х-18х+30у = 3+12
10х-6у+3х+15у-18х+6у = 0
-5х+30у = 15
-5х+15у = 0
30у = 15+5х
-5х+(15+5х)/2 = 0 |×2
30у = 15+5х
-10х+5х = -15
30у = 15+5х
-5х = -15
30у = 30
х = 3
у = 1
х = 3