vivek.kapoor83 wrote:but i just wanted to know..do we need to prove both the equations.
No, not quite. If |x| = |y|, there are four possibilities (you do not seem to be considering the last two below):
x, y both positive --> x = y
x, y both negative --> x = y
x positive, y negative --> x = -y
x negative, y positive --> x = -y
Which is why I said above that |x| = |y| is true if x = y or x = -y. Note that -x = -y is exactly the same equation as x=y (just multiply both sides by -1), so there is no need to consider it separately.
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