Prove Sin(a+b)=sin(a)cos(b)+cos(a)sin(b)

Prove Sin(a+b)=sin(a)cos(b)+cos(a)sin(b)

9 Answers

1
sindhu br ·

if u r familiar with the proof of cos(a-b) then u can use this....
sin(a+b)=cos(Î /2-(a+b))
=cos((Î /2-a)-b)
=coa(Î /2-a)cosb+sin(Î /2-a)sinb
=sin a cos b+sin b cos a

62
Lokesh Verma ·

no dear .. i am looking for a fundamental proof.. not this one..

i mean if u are using this result of cos (a-b) prove that!

I hope u understand what i am saying :)

1
sindhu br ·

I can prove that in two diff ways .........
is it fine , if I put it 2moro.
I got ur point..........

62
Lokesh Verma ·

ok great :)

1
AARTHI ·

is it usin vectors?ie cross pdt?if itz so then i can prove

62
Lokesh Verma ·

Yes i guess that should work as well :)

33
Abhishek Priyam ·

Both vectors have equal magnitude A

|A1XA2| by components.....
gives...

A2(cosa.sinb+sina.cosb)..........................(i)

now cross product by A2sin(a+b) ...............(AB sinθ)...........(ii)

from (i) and (ii) sin(a+b)=(cosa.sinb+sina.cosb).

..................................................................................................

1
AARTHI ·

yah even mine was like dis one

62
Lokesh Verma ·

Good work guys :)

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