The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

C3 Help needed

IMG_20130719_151238-1.jpg
I need help on q 13e. I expressed the LHS as

sinAcosB + sinBcosA
-----------------------
sinAcosB -sinBcosA

Now I'm not sure where to go:frown: and need some help please.

Thanks:smile:
Reply 1
Avatar for BabyMaths
BabyMaths
Original post by krisshP
IMG_20130719_151238-1.jpg
I need help on q 13e. I expressed the LHS as

sinAcosB + sinBcosA
-----------------------
sinAcosB -sinBcosA

Now I'm not sure where to go:frown: and need some help please.

Thanks:smile:


Divide top and bottom by something

Spoiler

Reply 2
Avatar for krisshP
krisshP
OP
14
Original post by BabyMaths
Divide top and bottom by something

Spoiler



Thanks for the quick reply :smile:, I've now proved the identity as required.
Reply 3
Avatar for krisshP
krisshP
OP
14
Original post by BabyMaths
Divide top and bottom by something

Spoiler



I wanted to just experiment so I divided top and bottom by sinAsinB and then with the result I multiplied top and bottom by tanAtanB and proved the identity again :tongue:
Reply 4
Avatar for krisshP
krisshP
OP
14
Original post by BabyMaths
Divide top and bottom by something

Spoiler



Would it be possible for you to help me in another question please?

Prove the following identity:
sin(A + B)sin(A-B) ≡ sin^2 A -sin^2 B

Here's my working out:

LHS ≡ (sinAcosB +sinBcosA)(sinAcosB-sinBcosA)

=(sinAcosB)^2 - (sinBcosA)^2

Any ideas on what to do next?

Thanks
Reply 5
Avatar for BabyMaths
BabyMaths
Original post by krisshP
Would it be possible for you to help me in another question please?

Prove the following identity:
sin(A + B)sin(A-B) ≡ sin^2 A -sin^2 B

Here's my working out:

LHS ≡ (sinAcosB +sinBcosA)(sinAcosB-sinBcosA)

=(sinAcosB)^2 - (sinBcosA)^2

Any ideas on what to do next?

Thanks


You have sin⁡2Acos⁡2B−sin⁡2Bcos⁡2A\sin^2 A \cos^2 B - \sin^2B \cos^2A

Replace each cos^2 with 1-sin^2, expand and simplify.
Reply 6
Avatar for krisshP
krisshP
OP
14
Original post by BabyMaths
You have sin⁡2Acos⁡2B−sin⁡2Bcos⁡2A\sin^2 A \cos^2 B - \sin^2B \cos^2A

Replace each cos^2 with 1-sin^2, expand and simplify.


That worked well :smile:

Thanks for all the help :biggrin:
Reply 7
Avatar for BabyMaths
BabyMaths
Original post by krisshP
That worked well :smile:

Thanks for all the help :biggrin:


No problem. :smile:

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you