f.2簡單simultaneous equantion~~

1. x + 2y = 12 ... (1)

x - 5y = -2 ... (2)

From equation (1), x = 12 - 2y ... (3)

Sub (3) into (2),

(12 - 2y) - 5y = -2

-7y = -2 - 12 = -14

y = 2

Put y = 2 into (3), x = 12 - 2(2) = 8


2. 3x + y = -1 ... (1)

9x + 2y = 1 ... (2)

From eqt (1), y = -1 - 3x ... (3)

Sub (3) into (2),

9x + 2(-1 - 3x) = 1

3x - 2 = 1

x = 1

Put x = 1 into (3), y = -1 - 3(1) = -4


3. x - 3y = -2 ... (1)

5x - 2y = 16 ... (2)

From eqt (1), x = -2 + 3y ... (3)

Put (3) into (2),

5(-2 + 3y) - 2y = 16

-10 + 15y - 2y = 16

13y = 26

y = 2

Put y = 2 into (3), x = -2 + 3(2) = 4

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