Trig Identities *PLEASE HELP*

jimmytwofingers · 2012-01-22 13:32:32

need help!!
these are a few questions i got wrong on homework... dont understand

Proof:

sec²x + csc²x = sec²x csc²x

((1+cosx)/sinx) + ((sinx)/(1+cosx)) = 2cscx

(1+secx)/(tanx + sinx) = cscx

(tanx-tany)/(cotx-coty) = -tanx tany

(cos(x-y))/(sinx cosy) = cotx + tany

Last edited by jimmytwofingers (2012-01-22 14:23:22)

bobbym · 2012-01-22 13:45:14

Hi jimmytwofingers;

Now combine using algebra.

bobbym · 2012-01-22 13:49:55

I know that, already done in post #2.

jimmytwofingers · 2012-01-22 13:57:27

thanks, only a few left now

Last edited by jimmytwofingers (2012-01-22 14:24:06)

bobbym · 2012-01-22 14:03:23

Add the two fractions on the LHS.

Clean up the LHS.

Cancel on the LHS.

bobbym · 2012-01-22 14:28:06

Multiply top and bottom by cos(x).

Cancel on the LHS.

jimmytwofingers · 2012-01-22 14:29:22

thanks so much bobbym,
think u can help me with 2 more?

bobbym · 2012-01-22 14:33:39

I am going to eat now, when I come back. Please post them in the meantime.

jimmytwofingers · 2012-01-22 14:36:19

ok i added them to post 1

bobbym · 2012-01-22 16:10:08

For the 4th one;

Multiply top and bottom of the LHS by tan(x)tan(y).

Multiply both sides by (tan(y)-tan(x)).

Multiply both sides by -1.

For the fifth one:

By a well known identity:
http://www.sosmath.com/trig/Trig5/trig5/trig5.html

second sum - difference formula. We have:

Math Is Fun Forum

#1 2012-01-22 13:32:32