# Tutor.com Functions Session

##### Dec. 13, 2012

Session Transcript - Math - Calculus, 11/11/2012 5:31PM - Tutor.comSession Date: 11/11/2012 5:31PM
Length: 18.9 minute(s)
Subject: Math - Calculus

System Message
[00:00:00] *** Please note: All sessions are recorded for quality control. ***

Greg (Customer)
[00:00:01] Help prove a trig identity. sinx-siny = 2cos([x+y]/2)sin([x+y]/2)

Roberto C (Tutor)
[00:00:07] Welcome to Tutor.com ! Let's get started.

Greg (Customer)
[00:00:20] Can you help me prove this trig identity?

Roberto C (Tutor)
[00:00:35] We can try! what properties have you learned so far?

Greg (Customer)
[00:00:48] I think most of them.

Roberto C (Tutor)
[00:01:18] I'm researching...

Greg (Customer)
[00:01:47] ok

Roberto C (Tutor)
[00:03:05] Okay I'm pretty lost here. I won't waste any more of your time. I can transfer you to someone who will be able to help you much more if you'd like!?

Greg (Customer)
[00:03:12] sure

System Message
[00:04:25] *** The session has been transferred. ***

Max W (Tutor)
[00:04:36] Welcome to Tutor.com ! Let's get started.

Greg (Customer)
[00:05:14] ok
[00:05:26] can you help me prove this trig identity?

Max W (Tutor)
[00:07:08] we can use the double angle formula for sine here

Greg (Customer)
[00:07:11] ok

Max W (Tutor)
[00:08:53] then we use the sine of the sum formula

Greg (Customer)
[00:08:50] how does 2cos(x+y/2).... equal sin(x+y)?

Max W (Tutor)
[00:10:01] review your double angle formula for sine but read it from right to left
[00:10:11] i have written it in light blue
[00:10:28] here A = (X+Y)/2

Greg (Customer)
[00:10:25] is sin2a part of the black equation?

Max W (Tutor)
[00:10:39] no
[00:11:49] registering now?

Greg (Customer)
[00:11:52] yes

Max W (Tutor)
[00:12:02] cool
[00:12:38] cosine of X is sine of (90 - X), right?

Greg (Customer)
[00:12:45] yes
[00:14:56] ok
[00:16:01] where would i go from here?

Max W (Tutor)
[00:16:30] i am thinking for a second
[00:18:01] I'm working on this...