In this instance we replace "v" with "x" and we replace "u" with "y".

x = y -5


x = 3y +7

I do that just to make it easier for me to understand.

Lets solve.


x = y -5

Substituation means you substitute side for side... So, if you want to solve for X (v) you need to add 5 to the right side to counter the negative 5.

'x = y -5
'+5 +5'

x +5 = y

y = 0

or U = 0

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