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C3 MEI help!

http://www.mei.org.uk/files/papers/c305ju_dskjtr.pdf

I can seem to do q8i.

xsin3x = 0

so sin3x = 0
So I take the arcsin of both sides

and end up with 3x = 0?

But the mark scheme says that sin3x = pi?

HELP!
Reply 1
Avatar for qgujxj39
qgujxj39
17
You can't just take the arcsin. You have to consider all of the possible solutions. Draw a graph of y=sin⁡3xy = \sin 3x, look at all the places where it cuts the x-axis, and you'll see what I mean.
Reply 2
Avatar for Wesssty
Wesssty
12
sin3x = 0 & x = 0.
sinpi = 0
3x must then equal pi.
x = pi/3.
Reply 3
Avatar for win2kpro
win2kpro
10
when does sin x = 0? just when x =0? - Draw a Sine graph to find out if you are unsure :p: I did this question about an hour ago haha :smile:
yeah I came across this problem. If you draw a sign graph you'll see that sin(pi) is 0
so you can go from there..

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