EVERYBODY HELPS ME

HELLO!I need HELP!!!!
I have a question about math past paper(c1,6663/01,10 WED JAN 2007)
question9,part C
I can`t show it ...I don`t know how to work out this question...

IF anybody has mark scheme`s answer or knows how to do it ,please show me in comments

THANKS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!