Prove the identities:

1.) cot (A + B) = (cotAcotB - 1) / (cotB + cotA)

2.) cot (A - B) = (cotAcotB + 1) / (cotB - cotA)

3.) sec (A + B) = (secAsecB) / (1 - tanAtanB)

4.) csc (A + B) = (cscAcscB) / (cotB + cotA)

Printable View

- August 26th 2006, 05:32 PM^_^Engineer_Adam^_^Nid help please
Prove the identities:

1.) cot (A + B) = (cotAcotB - 1) / (cotB + cotA)

2.) cot (A - B) = (cotAcotB + 1) / (cotB - cotA)

3.) sec (A + B) = (secAsecB) / (1 - tanAtanB)

4.) csc (A + B) = (cscAcscB) / (cotB + cotA) - August 26th 2006, 05:52 PMThePerfectHackerQuote:

Originally Posted by**^_^Engineer_Adam^_^**

Divide numerator and denominator by , thus,

- August 26th 2006, 05:56 PMThePerfectHackerQuote:

Originally Posted by**^_^Engineer_Adam^_^**

Multiply numerator and denominator by (-1):

- August 26th 2006, 05:59 PMThePerfectHackerQuote:

Originally Posted by**^_^Engineer_Adam^_^**

Divide numerator and denominator by

Thus,

- August 26th 2006, 06:02 PMThePerfectHackerQuote:

Originally Posted by**^_^Engineer_Adam^_^**

Divide numerator and denominator by

Thus,

- August 27th 2006, 12:54 AM^_^Engineer_Adam^_^Quote:

Originally Posted by**ThePerfectHacker**

how come cot (x-y) became equal to cot (x-(-y)) ? - August 27th 2006, 01:00 AMGlaysherQuote:

Originally Posted by**^_^Engineer_Adam^_^**

Then he uses the answer from part (a) - August 27th 2006, 06:14 AMThePerfectHacker
Problem Fixed, thank you for noticing.