Question

Solve the system by substitution

3x=4y-13

9x-y=12

Answer 1

Substitution method

Given equations are 3x = 4y-13 ---> (1)

9x-y = 12

Subtract 9x from each side.

-y = -9x+12

Divide to each side by negitive one.

y = 9x-12 ---> (2)

From (2) substitute the y value in (1).

3x = 4(9x-12)-13

3x = 36x-48-13

3x = 36x-61

Subtract 36x from each side.

-33x = -61

Divide to each side by negitive 33.

x = -61/-33

⇒ x = 61/33

Substitute the x value in (1).

3(61/33) = 4y-13

61/11 = 4y-13

Add 13 to each side.

61/11+13 = 4y

(61+143)/11 = 4y

204/11 = 4y

204/44 = y

⇒ y = 51/11

Solution x = 61/33, y = 51/11.