mwilt Posts: 3, Reputation: 1 New Member #1 Mar 4, 2009, 08:59 PM
trig proofs
how do you prove

cosx+sinxtanx=secx
 Perito Posts: 3,139, Reputation: 150 Ultra Member #2 Mar 5, 2009, 05:55 AM

The usual way to prove any of these trig identities is to convert everything to sines and cosines and simplify. Sometimes you have to be cleaver.

cos(x) + sin(x) tan(x) = sec(x)

identity: tan(x) = sin(x) / cos(x)

cos(x) + sin(x) * sin(x)/cos(x) = 1/cos(x)
cos(x) + sin^2(x)/cos(x) = 1/cos(x)
[cos^2(x) + sin^2(x)] / cos(x) = 1 / cos(x)

identity: sin^2(x) + cos^2(x) = 1

identity: sec(x) = 1/cos(x)

sec(x) = sec(x)

quod erat demonstrandum

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