Question

We always subtract same number from both sides LHS and RHS.
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Answer 1

When same number is subtracted from both the sides of equation i.e. L.H.S. and R.H.S of the equation, the equality still holds true. "When same number is subtracted both the sides of equation, equality still holds true."

Answer 2

no it is not necessary .but in some cases if we have to equalise both the sides of the equation