How do you solve x+y=-1 and x-y=3?

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Answer 1 · 2015-11-04T05:52:50

$color(green)(x = 1$
$color(green)(y = -2$

$x + y = -1$ -------(1)
$x - y = 3$ -------(2)

By asking us to solve, the question is indirectly asking us for the value of $x and y$

To get the value of $x$ , let's ADD the two equations. Because ADDING will help us eliminate $y$ with ease.

$(x + y) + (x - y) = -1 + 3$

$x + cancel(y) + x - cancel(y) = 2$

$2x = 2$

Dividing both sides by 2, we get

$(cancel(2)x)/cancel(2) = 2/2$

$color(green)(x = 1$

Now to get the value of $y$ can simply substitute this value of $x$ in any of the two equations

Substituting $x = 1$ in the first equation, we get

$1 + y = -1$

Transposing 1 to the right hand side, we get

$y = -1 -1$

$color(green)(y = -2$