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Find the value of
x+(x-y)=71
y-(x-y)=5
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You probably want to say "Find the solution of the system".
x + (x-y) = 71, (1)
y - (x-y) = 5. (2)
Add eqns (1) and (2). You will get
x + y = 76. (1')
Now distract eqn.(2) from the eqn.(1). You will get
3(x - y) = 66. (2')
Next divide (2') by 3 (both sides). You will get an equivalent system
x + y = 76, (1'')
x - y = 22. (2'').
Now add (1'') and (2''). You will get
2x = 98 ---> x = = 49.
Then from (1'') y = 76 - x = 76 - 49 = 27.
Answer. x = 49, y = 27.