# Trig Identities A Level Maths

Watch
Announcements
#1
Does anyone know how to solve this
(a) Write down formulae for sin (A + B) and sin (A – B).

Using X = A + B and Y = A – B, prove that
sin X + sin Y = 2 sin(X+Y/2) cos (X+Y/2)

I'm super confused? Thanks
0
1 month ago
#2
(Original post by violetblue253)
Does anyone know how to solve this
(a) Write down formulae for sin (A + B) and sin (A – B).

Using X = A + B and Y = A – B, prove that
sin X + sin Y = 2 sin(X+Y/2) cos (X+Y/2)

I'm super confused? Thanks
They're asking you to derive the sum-to-product formulae from formulae you already know Can you do the first part - expand sin(A+b) and sin(A-B) ?
0
#3
(Original post by davros)
They're asking you to derive the sum-to-product formulae from formulae you already know Can you do the first part - expand sin(A+b) and sin(A-B) ?
Yeah I did that and I got
sin X + sin Y = 2sinAcosB + cosAsinB - cosAsinB
sin X + sin Y = 2sinAcosB
idk what to do after that though
0
1 month ago
#4
(Original post by violetblue253)
Yeah I did that and I got
sin X + sin Y = 2sinAcosB + cosAsinB - cosAsinB
sin X + sin Y = 2sinAcosB
idk what to do after that though
Well if X = A + B and Y = A - B, can you solve these as if they were simultaneous equations to write A = something in terms of X and Y and the same for B?
0
#5
(Original post by davros)
Well if X = A + B and Y = A - B, can you solve these as if they were simultaneous equations to write A = something in terms of X and Y and the same for B?
Got it thank you!!
1
X

new posts Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### Should there be a new university admissions system that ditches predicted grades?

No, I think predicted grades should still be used to make offers (707)
33.94%
Yes, I like the idea of applying to uni after I received my grades (PQA) (890)
42.73%
Yes, I like the idea of receiving offers only after I receive my grades (PQO) (393)
18.87%
I think there is a better option than the ones suggested (let us know in the thread!) (93)
4.46%