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How Do You Solve 3x+5y=19 And -4x+y=17 Using The Substitution Method?

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Oddman answered
The only variable with a coefficient of 1 is y in the second equation. Solving that equation for y involves the fewest steps, so we start there.
-4x + y = 17
y = 17 + 4x (add 4x to both sides)

Now, we substitute this for y in the first equation.
3x + 5(17 + 4x) = 19
3x + 85 + 20x = 19 (use the distributive property)
23x = -66 (subtract 85 from both sides, collect terms)
x = -66/23 (divide both sides by 23)
x = -2 20/23 (express as a mixed number)

y = 17 + 4(-66/23) (put x into our equation for y)
y = (23*17 - 4*66)/23 (combine terms)
y = (391 - 264)/23 (simplify)
y = 127/23 (simplify)
y = 5 12/23 (express as a mixed number)

The solution is (x, y) = (-2 20/23, 5 12/23)

Check
3(-2 20/23) + 5(5 12/23) = 19
-8 14/23 + 27 14/23 = 19 (yes)

-4(-2 20/23) + (5 12/23) = 17
11 11/23 + 5 12/23 = 17 (yes)
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