Verify these: [i need help getting started and other help you can throw at me]

1) sin(x + y)cos y - cos (x + y)sin y = sin x

2) cot x = (cos3x + cos x) / (sin 3x - sin x)

3) tan(B/2) = sec B / (sec B csc B + csc B)

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- November 7th 2009, 10:26 PMJohnny Walker BlackNeed 3 Homework problems
Verify these: [i need help getting started and other help you can throw at me]

1) sin(x + y)cos y - cos (x + y)sin y = sin x

2) cot x = (cos3x + cos x) / (sin 3x - sin x)

3) tan(B/2) = sec B / (sec B csc B + csc B) - November 7th 2009, 10:45 PMDebsta
Look up (and learn) the expansion rules for sin(a+b), cos(a+b), tan(a+b), sin (a-b),

sin2a, etc. And apply them here. Have a go or you'll never never know. - November 8th 2009, 07:50 AMGrandad
Hello Johnny Walker BlackHere's the method for each one:

1) Use the identities below to expand the LHS:

2) Use the identities:

3) Get rid of and (horrible things!) by multiplying top-and-bottom of the fraction by , using the fact that:andThen use:

Grandad