Question 560027
x+y=7..........(1) 
x-y=5..........(2)

Add (1) and (2)
x+y=7 
x-y=5
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2x=12
2x/2=12/2
x=6
Put the value of x in (1)
x+y=7
6+y=7
y=7-6
y=1

x,y=6,1

Check
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Put the values of x and y in (1)
x+y=7
6+1=7
7=7
Put the values of x and y in (2)
x-y=5
6-1=5
5=5