maths

Former Member

Is there a whizz kid that can explain to me the context between:

sin(A+B) = sinA*cosB + cosA*sinB ???

I just don't get it. I browsed various webpages, but I couldn't follow the explanation.

Can someone explain it in a easy-to-follow fashion?

Thanks in advance.

Former Member

Hey. I found a fairly simple explaination from my A-level maths notes. I can try to scan it or expalin it if you want although im not exactly great at explaining things.

It basically shows how you get from sin (A+B) to sinAcosB + cosAsinB.

Former Member

Firefly-86 wrote:

Hey. I found a fairly simple explaination from my A-level maths notes. I can try to scan it or expalin it if you want although im not exactly great at explaining things.

It basically shows how you get from sin (A+B) to sinAcosB + cosAsinB.

Oh yes, please do...

Former Member

Ive got to draw a picture so I may be a while in replying.

Former Member

Firefly-86 wrote:

Ive got to draw a picture so I may be a while in replying.

This reminds me of the times I gave private lessons in physics over ICQ and drew a lot of MS Paints about the concepts of motors and generators
and other different stuff. I got the still saved here

I was amazing
"whoa, dude... Where do you get all the pictures from?"
"I draw them, while we speak."
"Wow..."

Thanks in advance, dude.

Former Member

Right.

This is how ive got it in my notes:

Sin A = TS/OT

Sin B = PT/OP

Cos A = PQ/PT

Cos B = OT/OP

Right Now the proof.

Sin(A+B) = (PR)/(OP)

Sin(A+B) = (PQ + QR)/(OP)

Sin(A+B) = (PQ + TS)/(OP)

Sin(A+B) = (PQ/OP)+(TS/OP)

Sin(A+B) = (PQ/PT)*(PT/OP)+(TS/OT)*(OT/OP)

this gives:

Sin(A+B) = cosA sinB + sinA cosB

Any questions?

Former Member

Firefly-86 wrote:

Right.

nightmare

Any questions?

Yeah, I kinda am able to follow it.

thanks.

Former Member

No worries. Glad to be of use to someone.

Former Member

Draw yourself some triangles nicely labelled up to look at while you try it, that should help too.

Former Member

The picture does help while trying to understand whats going on.

In fact its fairly essential to understand it.

Besides I think I did quite well for 10 minutes work in paint.

Former Member

Cos A = PQ/PT

I don't get that one.
This is the cosinus of the very little triangle PQT.

not the one of A...

The other things are coherent, but this...

/e:
Yeah, I got it now... but it's pretty complicated. I won't be able to reconstruct that in maths, when I am called to the blackboard

I needed to calculate a "x" WITHOUT calculator so that

arcsin x = arcsin 1/3 + arcsin 4/5.
I conclude

sin(arcsin 1/3 + arcsin 4/5) = x

So I need this formula here for sin(A+B), where A is arcsin 1/3, and B is arcsin 4/5.
We didnot do it in the lectures, and I couldn't find it in our formula book.

I just tell him I found the answer in the endless abyss of the data superhighway the Interbutt, and he's going to accept it.

Former Member

E=Mc2.

Former Member

StrubbleS wrote:

I don't get that one.
This is the cosinus of the very little triangle PQT.

not the one of A...

The other things are coherent, but this...

/e:
Yeah, I got it now... but it's pretty complicated. I won't be able to reconstruct that in maths, when I am called to the blackboard

I needed to calculate a "x" WITHOUT calculator so that

arcsin x = arcsin 1/3 + arcsin 4/5.
I conclude

sin(arcsin 1/3 + arcsin 4/5) = x

So I need this formula here for sin(A+B), where A is arcsin 1/3, and B is arcsin 4/5.
We didnot do it in the lectures, and I couldn't find it in our formula book.

I just tell him I found the answer in the endless abyss of the data superhighway the Interbutt, and he's going to accept it.

Ah I see its a small thing Known as Z angles. Basically angle S O T is the same as angle O T Q which is the same as angle T P Q. So you can say that Cos A is PQ/PT