Posted by **Cyndy** on Friday, August 3, 2012 at 3:39pm.

Find the counterexample to shows that the equation sec (alpha) - cos (alpha) = sin (alpha) sec (alpha) is not an identity.

Please explain.

- Trigonometry -
**Steve**, Friday, August 3, 2012 at 3:55pm
there are many counterexamples. For instance,

sec(pi/4) - cos(pi/4) = √2 - 1/√2

sin(pi/4)*sec(pi/4) = 1/√2 * √2 = 1

not equal. In fact, for any alpha not a multiple of pi, they are not equal.

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