i don't have a clue on how to even start part (a)

any help would be much appreciated

**1**

# 2003 - paper 1 - question 10

Started by xClairex, May 13 2007 02:31 PM

7 replies to this topic

### #1

Posted 13 May 2007 - 02:31 PM

### #2

Posted 13 May 2007 - 03:41 PM

Ok, for 10.a.(i). ...draw a line down from point A to the x axis an call it B so u make a triangle. This means u have 3 points, O(0,0), A (8,4) and B(8,0) ...now the distance from O to A is 8, and from A to B is 4, so u use pythagoras's thereom to work out the distance from O to A which turns about to be the square root of 80 ...then u use SOHCAHTOA to work out sin(p) which = (8/square root of 80) an cos(p) which = (4/square root of 80) ...then u use the double angle formula so that sin(2p) = 2sin(p)cos(p) ...then substitute in ur answers an u shud get 2((8/square root of 80)(4/square root of 80) which = 64/80, an then if u divide both by 16, u get 4/5

As For 10.b.(ii), im still tryin 2 work that 1 out but i'll let u no when i get it

As For 10.b.(ii), im still tryin 2 work that 1 out but i'll let u no when i get it

### #4

Posted 13 May 2007 - 03:54 PM

i managed 2 work out 10.a.(ii) but i got -3/5 an the answer is 3/5 but i'll tell u how i worked it out an if u spot where i've went wrong, let me no ...use the double angle formula again so that cos(2p) = 1-2sin(squared)p ...then substitute the sin(p) value from part (i) so u get 1-2(8/square root of 80)squared ...this then becums 1-2(64/80) which equals 1-2(4/5) and then 1-8/5 which after u take 5 as the common denominater, gives u -3/5 ...hope thats helped a bit.

### #5

Posted 13 May 2007 - 04:01 PM

yeah thanks this has helped alot

i now see how to get (ii) as -3/5 but i cant see how it would be positive :S

i now see how to get (ii) as -3/5 but i cant see how it would be positive :S

### #6

Posted 13 May 2007 - 04:08 PM

10 a ii) should work like this:

Azie: your error arises with your substitution of : your squaring is slightly off. It's a simple error, but it's what's causing all the problems

Azie: your error arises with your substitution of : your squaring is slightly off. It's a simple error, but it's what's causing all the problems

### #7

Posted 13 May 2007 - 04:13 PM

ah, i c where i went wrong now, thanks

### #8

Posted 13 May 2007 - 04:19 PM

thank you pete and azie

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