Real analysis
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29.2 Prove that |cos x - cos y| ≤ |x - y| for all x, y in R
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Solution Summary
This is a proof regarding cosx and cosy for x, y in R.
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29.2 Prove that |cos x - cos y| ≤ |x - y| for all x, y in R.
Solution:
In order to prove the above statement, we need to prove first some trigonometric basic formulas.
1) Let's prove the identity:
( 1)
Proof:
We start from the basic formulas:
( 2)
( 3)
By subtracting first equality from the second one, we will have
( 4)
We denote now
( 5)
By adding the 2 equations, one ...
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