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The Edexcel C3 (14/06/12 - AM) Revision Thread

Find in terms of pi, the solutions of the equation:

Sin(5X) + Sin(X) =0

for the x interval, 0<=(X)<pi

This is straight off a Solomon paper, and was wondering if a question like this can come up in an edexcel paper for C3 as I havent seen a question like it in any past papers.

Think about the for trigonometric identity:

sin A + sin B = 2 sin [(0.5)A + B] cos [(0.5)A − B]

Where A = 5x AND B = x

Hope that Helps!

(edited 11 years ago)

Reply 21

jlnbello

For proof questions in C3 and C4 etc. If you can't show that X=Y can you do the reverse and show that Y=X.
Will you get marked down? I mean its still showing that one form is identical to the other. I am just asking because sometimes when i do past papers involving proof i get mindblocked and just do the reverse of what they are telling me.

Reply 22

NutterFrutter

Need to do well in C3. Got a B in January. :frown:

Reply 23

NutterFrutter

Original post by jlnbello

For proof questions in C3 and C4 etc. If you can't show that X=Y can you do the reverse and show that Y=X.
Will you get marked down? I mean its still showing that one form is identical to the other. I am just asking because sometimes when i do past papers involving proof i get mindblocked and just do the reverse of what they are telling me.

That's fine, as long as you can show that one side equals the other side then you have proven it.

Generally, you use the side that looks the most diffucult to prove the other side.

Reply 24

jlnbello

Original post by NutterFrutter

That's fine, as long as you can show that one side equals the other side then you have proven it.

Generally, you use the side that looks the most diffucult to prove the other side.

phew thanks man :smile:

Reply 25

Eternal*

14

Anyone here resitting from Jan ?

Reply 26

NutterFrutter

Original post by Eternal*

Anyone here resitting from Jan ?

Yup.

Reply 27

otrivine

14

do you guys think this would be easier or harder paper ?

Reply 28

NutterFrutter

Original post by otrivine

do you guys think this would be easier or harder paper ?

I think it will be slightly more difficult than the January paper as that had higher than normal grade boundaries.

Reply 29

otrivine

14

Original post by NutterFrutter

I think it will be slightly more difficult than the January paper as that had higher than normal grade boundaries.

like cause this is my first time taking c3 ! i mean like how much harder can they make it cause i looked at like previous past papers the questions look similar just different numbers>?

Reply 30

Eternal*

14

Original post by NutterFrutter

Yup.

Original post by otrivine

do you guys think this would be easier or harder paper ?

Harder, because there are more people doing it...

Why have I got negged??????

(edited 11 years ago)

Reply 31

hippogriff

Original post by StraightUpG

Find in terms of pi, the solutions of the equation:

Sin(5X) + Sin(X) =0

for the x interval, 0<=(X)<pi

This is straight off a Solomon paper, and was wondering if a question like this can come up in an edexcel paper for C3 as I havent seen a question like it in any past papers.

Solomon papers have a repuatation for being a lot above the standard of edexcel papers. I think it would be very unlikely for you to get a question like this in your paper, but just in case:

Let A = 5X and B = X

Sin(A) +Sin (B) = 0

Sin A + Sin B = 2 Sin((A + B)/2) Cos((A − B)/2) = 0 This is in the Core 3 formula booklet, which you will be given in the exam.)

Substituting X and 5X back in:

2 Sin((5X + X)/2) Cos((5X - X)/2) = 0

2 Sin (3X) Cos (2X)=0

Sin (3X) Cos (2X)=0

Therefore:

EITHER Sin(3X) = 0

X = pi/3 or 2pi/3 (0 and pi excluded because they are JUST outside the range.)

OR Cos(2X) = 0

X = pi/4 or 3pi/4

Therefore:

the solutions of the equation

Sin(5X) + Sin(X) =0

for the x interval, 0< X <pi are

X = pi/4, pi/3, 2pi/3, and 3pi/4

I hope this helps :smile:

Reply 32

hippogriff

Original post by Amy-Chod

Think about the for trigonometric identity:

sin A + sin B = 2 sin [(0.5)A + B] sin [(0.5)A − B]

Where A = 5x AND B = x

Hope that Helps!

This isn't correct

sin A + sin B = 2 sin [(0.5)A + B] COS [(0.5)A − B]
,not 2 sin [(0.5)A + B] SIN [(0.5)A − B]

By the way, this formula is on the Edexcel formula booklet, which you will be given in the exam, so you will NOT need to learn this, don't worry!