C1 and C2 DOUBTS HERE!!!!!

[MasterMath]

Woking on it now.

It opened but why is the syllabus number 6663 ? mines 6664 written on the paper >_<

[halosh92]

It opened but why is the syllabus number 6663 ? mines 6664 written on the paper >_<

those are practice papers their not pastpapers for edexcel

[MasterMath]

those are practice papers their not pastpapers for edexcel

Okay you expand Sin(X) which is equal to Sin(A+B)= SinACosB + SinBCosA and expand Sin(Y) which is equal to Sin(A-B)=SinACosB -SinBCosA .. then add them cause they said Sin(X) + Sin (Y) which gives 2SinACosB .. then im stuck >_<

[MasterMath]

Okay you expand Sin(X) which is equal to Sin(A+B)= SinACosB + SinBCosA and expand Sin(Y) which is equal to Sin(A-B)=SinACosB -SinBCosA .. then add them cause they said Sin(X) + Sin (Y) which gives 2SinACosB .. then im stuck >_<

oh i got it ! .. X+Y / 2 .. is A .. check it from the equation .. and X-Y/2 is B ! .. so just replace and here you go!

[MasterMath]

oh i got it ! .. X+Y / 2 .. is A .. check it from the equation .. and X-Y/2 is B ! .. so just replace and here you go!

Cause X = A+B .. and Y= A-B .. so X + Y = 2A .. but we want it A so divide by 2.. same for X-Y

[MasterMath]

And for b) .. i dont see any variable in the equation O_O . what are we supposed to solve for >_<

[halosh92]

And for b) .. i dont see any variable in the equation O_O . what are we supposed to solve for >_<

for the a) part where do they get the cos from :S
and part b) the zero is the thita its a typing error

[MasterMath]

for the a) part where do they get the cos from :S
and part b) the zero is the thita its a typing error

okay ill slowly explain part a) .. They said X=A+B .. and Y=A-B .. and then they said sin(X) + sin(Y) = ignore this part now..
sin(X) = sin(A+B) substitution.
sin(Y) = sin(A- B) substitution.
Now lets work with the expansion of sin(A+B) = sinAcosB +sinBcosA
and sin(A-B)= sinAcosB -sinBcosA..
okay now lets get back to the formula..
sin(X) + sin(Y) = sin(A+B) + sin(A-B) = sum of expansions= sinAcosB + sinBcosA + sinAcosB -sinBcosA = sinAcosB + sinAcosB=2sinAcosB..
okay all good till now?

[MasterMath]

We got 2sinAcosB but they wrote its equal to 2sin(X+Y/2)cos(X-Y/2)
So A must be equal to X+Y/2 .. and B must be equal to X-Y/2 .. to verify this lets try adding X and Y and dividing by 2 ..we should get A ..
X= A+B Y = A-B .. X+Y =A+B+A-B=2A .. then divide by 2 .. = A!!!
So our equation is correct .. so we can simply replace A by X+Y/2 and B by X-Y/2 .. so we reached the final equation they wanted!
Got it?

[halosh92]

okay ill slowly explain part a) .. They said X=A+B .. and Y=A-B .. and then they said sin(X) + sin(Y) = ignore this part now..
sin(X) = sin(A+B) substitution.
sin(Y) = sin(A- B) substitution.
Now lets work with the expansion of sin(A+B) = sinAcosB +sinBcosA
and sin(A-B)= sinAcosB -sinBcosA..
okay now lets get back to the formula..
sin(X) + sin(Y) = sin(A+B) + sin(A-B) = sum of expansions= sinAcosB + sinBcosA + sinAcosB -sinBcosA = sinAcosB + sinAcosB=2sinAcosB..
okay all good till now?

ok i got the expansion and all the other things but one tiny thing :
"Now lets work with the expansion of sin(A+B) = sinAcosB +sinBcosA"
shouldnt the expansion be sinA + SinB
where does the cos come from??? or is there some kind of rule?

[MasterMath]

ok i got the expansion and all the other things but one tiny thing :
"Now lets work with the expansion of sin(A+B) = sinAcosB +sinBcosA"
shouldnt the expansion be sinA + SinB
where does the cos come from??? or is there some kind of rule?

Yes there is a rule for sin(X+Y)= sinXcosY +sinYcosX for any values of X and Y.. and also sin(X-Y)=sinXcosY -sinYcosX ... you got to memorize those .. and here are some more
cos(X+Y)=cosXcosY -sinXsinY cos(X-Y)= cosXcosY +sinXsinY
tan(X+Y)=(tanX+ tanY)/1-tanXtanY  tan(X-Y)=(tanX-tanY)/1+tanXtanY
and more more..
Sin2x= 2sinxcosx
Cos2x= Cos²x-sin²x which is also equal to = 1-2sin²x = 2cos²x-1
and tan2x= 2tanx/1-tan²x

[MasterMath]

Yes there is a rule for sin(X+Y)= sinXcosY +sinYcosX for any values of X and Y.. and also sin(X-Y)=sinXcosY -sinYcosX ... you got to memorize those .. and here are some more
cos(X+Y)=cosXcosY -sinXsinY cos(X-Y)= cosXcosY +sinXsinY
tan(X+Y)=(tanX+ tanY)/1-tanXtanY  tan(X-Y)=(tanX-tanY)/1+tanXtanY
and more more..
Sin2x= 2sinxcosx
Cos2x= Cos²x-sin²x which is also equal to = 1-2sin²x = 2cos²x-1
and tan2x= 2tanx/1-tan²x

I have more , here are some .. dunno if needed for C2 maybe C3 ..
X= (P+Q)/2  .. Y=(P-Q)/2
sinp + sinq = 2sinXcosY
sinp -  sinq= 2cosXsinY
cosp + cosq =2cosXcosY
cosP - cosq= -2sinXsinY

[halosh92]

Yes there is a rule for sin(X+Y)= sinXcosY +sinYcosX for any values of X and Y.. and also sin(X-Y)=sinXcosY -sinYcosX ... you got to memorize those .. and here are some more
cos(X+Y)=cosXcosY -sinXsinY cos(X-Y)= cosXcosY +sinXsinY
tan(X+Y)=(tanX+ tanY)/1-tanXtanY  tan(X-Y)=(tanX-tanY)/1+tanXtanY
and more more..
Sin2x= 2sinxcosx
Cos2x= Cos²x-sin²x which is also equal to = 1-2sin²x = 2cos²x-1
and tan2x= 2tanx/1-tan²x

OMG THANKYOU SO MUCH
  but i never took any of this r u sure this is AS 

am rili sorry for the trouble thx again 

[MasterMath]

OMG THANKYOU SO MUCH
  but i never took any of this r u sure this is AS 

am rili sorry for the trouble thx again 

yep all those are needed , they'll help you atleast instead of proving them in the exam!

[Saladin]

This is from the old syllabus, this is now in C3. You do not need to know it.