How do you solve the linear system using substitution x = 16 - 4yx=16−4y and 3x + 4y = 83x+4y=8?

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Don't Memorise
Jun 5, 2015

x = color(blue)(16 - 4yx=16−4y ......equation (1)(1)

3x + 4y = 83x+4y=8.........equation (2)(2)

substituting equation (1)(1) in equation (2)(2)
3color(blue)((16-4y)) + 4y = 83(16−4y)+4y=8

48 - 12y + 4y = 848−12y+4y=8
48 - 8y= 848−8y=8
- 8y= 8-48 = -40−8y=8−48=−40
y=-40/-8y=−40−8
color(blue)(y=5y=5

substituting color(blue)(yy in equation (1)(1) to find xx
x =16 - 4yx=16−4y
x =16 - 4.5 = 16-20x=16−4.5=16−20
color(blue)(x = -4x=−4

the solution for the system of equations is
color(blue)(x= -4 and y = 5x=−4andy=5

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