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# FP1 Question - Attempt at your own risk watch

1. FP1 question on complex numbers. really annoying question

4.

z= -4+6i

The complex number w is given by w = A/(2-i), where A is a positive constant. Given that |w|= (root)20

(b) Find w in the form a+ib, where a and b are constants,

(c) calculate arg w/z
2. (Original post by zaini_attack)
FP1 question on complex numbers. really annoying question

4.

z= -4+6i

The complex number w is given by w = A/(2-i), where A is a positive constant. Given that |w|= (root)20

(b) Find w in the form a+ib, where a and b are constants,

(c) calculate arg w/z
for part a, you just use inverse tan of 6/4. and then add pi to it, as it is on the other side.
3. if nobody answers this by midnight then PM me and i will do it for you
i cba doing it now because its pretty simple stuff and you could find the answer in any textbook
4. bump bump bump
5. fine well answer to first question is 2.15879...
2.159 (3.d.p)
method; get gfx calculator
press math
across twice to CPX
down to "angle("
press enter
press -4+6i
press enter
truncate answer to 3dp with roundng
6. part C is exactly the same
and for part B you need to remember how you get mod Z, draw an argand plane (or plain? hah) and then consider how the value of root20 could be made...
7. WOOOOOW. thanks alot. any help with the rest.
8. sorry but i cba doing B for you because it would take me more than about 3 seconds and im going to bed now.. ill do it for you tomorrow night if nobody has still answered
9. loooool. thanks alot anywayz
10. its fine FP1 is by far my fave module so far
cba with stuff like C1 its just boring and i always drop a crap load of marks because i dont think about what im doing lol
11. w = A/(2-i) = A(2+i)/(2-i)(2+i) = (2A + Ai)/5, abs(w)=sqrt((2A/5)^2+(A/5)^2) = sqrt(5A^2/25) = sqrt(A^2/5), now recall that abs(w)=sqrt(20) then we must have that 20=A^2/5, A^2 = 100 => A = +/- 10, however, A>0 so A = 10
12. im pretty sure this is FP2 complex numbers
13. (Original post by blackdragonthegreat)
im pretty sure this is FP2 complex numbers
This is far too easy for fp2...
14. (Original post by blackdragonthegreat)
im pretty sure this is FP2 complex numbers
Definately FP1
15. For c I get:

Anybody care to confirm this?

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