I know the identities by hard. My problem is when its in fraction form with a radical. When do you multiply by conjugate and when not? (See picture for problem with tangent)

Second problem I tried to use sine of sum identity (picture with words)

Printable View

- June 29th 2013, 06:58 PMMelcarthusSum and Didderence Identities w/Pictures
I know the identities by hard. My problem is when its in fraction form with a radical. When do you multiply by conjugate and when not? (See picture for problem with tangent)

Second problem I tried to use sine of sum identity (picture with words) - June 29th 2013, 08:38 PMmpx86Re: Sum and Didderence Identities w/Pictures
tan 195 = tan ( 180 + 15) = tan 15

use tan 15= tan(45-30)

and get ur answer.... - June 29th 2013, 08:44 PMmpx86Re: Sum and Didderence Identities w/Pictures
sin(A+B)=sinA cosB +cosA sinB

sin A= 3/5

sin B =5/13

as A is in second quadrant

therefore cos will be negative

cos A = -4/5

cos B =12/13

can u find sin (A+B) now? - June 29th 2013, 09:27 PMibduttRe: Sum and Didderence Identities w/Pictures
- June 30th 2013, 06:05 AMMelcarthusRe: Sum and Didderence Identities w/Pictures
- June 30th 2013, 09:05 AMMelcarthusRe: Sum and Didderence Identities w/Pictures
You probably used the Sine pythag identity

- June 30th 2013, 09:15 AMMelcarthusRe: Sum and Didderence Identities w/Pictures
I got it now thanks.