Question 299044
1) -x-y=8
 -(2x-y=-1)
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-3x=9
x=9/-3
x=-3 ans. 
-(-3)-y=8
3-y=8
-y=8-3
y=-5 ans.
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2) x+y=-7  
 -(3x+y=-9)
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-2x=2
x=2/-2
x=-1 ans.  
-1+y=-7
y=-7+1
y=-6 ans.
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I'll leave the remaing 2 for you to practice with.
3) x+3y=19  x-y=-1 [ans. x=4 & y=5]
4) 3x-3y=-15 3x+3y=3 [ans. x=-2 & y=3]