a)
2x - 9y = -1 (×5)
-10x - 7y = 2
10x - 45y = -5 => 10x = -5 + 45y
-(-5 + 45y) - 7y = 2
5 - 45y - 7y = 2
-52y = 2- 5
-52y = -3
y = 3/52
2x - 9(3/52) = -1
2x - 27/52 = -1
2x = - 52/52 + 27/52
2x = -25/52
x = -25/104
b)
3x - 6y = -3
x + 9y = -4 => x = -4 - 9y
3(-4 - 9y) - 6y = -3
-12 - 27y - 6y = -3
-33y = -3 + 12
-33y = 9
y = -9/33
x = -4 - 9(-9/33)
x = -4 + 81/33
[tex]x = - \frac{132}{33} + \frac{81}{33} [/tex]
[tex]x = - \frac{51}{33} [/tex]
c)
4a - b = 9 => 4a - 9 = b
-6a + 9b = -3
-6a + 9(4a - 9) = -3
-6a + 36a - 81 = -3
30a = -3 + 81
30a = 78
a = 2,6
b = 4(2,6) - 9
b = 10,4 - 9
b = 1,4