What is 3x-y=4 and x+y=8 substitution?

Question

Answer

Add together the equations to get rid of y leaving you with 4x = 12 meaning x = 3. Put this into one of the original equations for example 3 + y = 8 so y = 5. I think this is what you meant?

Answer

3x - y = 4
x + y = 8  Add spaces to improve readability.

Choose one equation and solve for one unknown.

x + y = 8  The rule is you can do any valid operation on both sides of an equation and it will still be equal. Subtract x.

y = 8 - x  Substitute this for y in the other equation.

3x - y = 4

3x - 8 + x = 4  Simplify and add 8.

4x = 12  Divide by 4.

x = 3

The other way to solve this is called elimination. Adjust the equations so you can add them to eliminate one variable.

3x - y = 4
x + y = 8  No adjustment required.
------------  ADD
4x ___= 12
x = 3  SAME ANSWER.

What is 3x-y=4 and x+y=8 substitution?

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