How do you solve the system $y-x=-1, x+y=8$ ?

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Answer 1 · 2016-11-27T20:05:46

{x,y}={4.5,3.5}

$y-x=-1" "(1)$

$x+y=8" "(2)$

$"the sum of left sides of equations (1) ,(2)"$

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

$"the sum of right sides of equations (1),(2)"$

$-1+8=7$

$2y=7$

$y=7/2=3.5$

$"now use (1) or (2)"$

$3.5-x=-1$

$x=3.5+1=4.5$

How do you solve the system y-x=-1, x+y=8y-x=-1, x+y=8?