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C3 help :)

Can someone help me with 7iii?
Not sure what to do. I tried doing that sign change thing but both answers were positive. When I put x=1.8 and x=1.9 in.
Clue: x - 1 = cos(x/3)
Original post by Super199
Can someone help me with 7iii?
Not sure what to do. I tried doing that sign change thing but both answers were positive. When I put x=1.8 and x=1.9 in.

Do you have your calculator set to radians?
Reply 3
Original post by shawn_o1
Clue: x - 1 = cos(x/3)


I don't get how you got to that?
Reply 4
Original post by Malgorithm
Do you have your calculator set to radians?

Yh. When I put x=1.9 I get 1.353
X=1.8 gives 1.93
Original post by Super199
I don't get how you got to that?


Try calculating 1 + cos(1.8/3) and 1 + cos(1.9/3) instead
Reply 6
Original post by shawn_o1
Try calculating 1 + cos(1.8/3) and 1 + cos(1.9/3) instead


Lol I've been daft yh got it now I think. You have to rearrange for x right?
Original post by Super199
Lol I've been daft yh got it now I think. You have to rearrange for x right?


Yep
Reply 8
Original post by shawn_o1
Try calculating 1 + cos(1.8/3) and 1 + cos(1.9/3) instead


I've done it now but I swear that doesn't help does it?
I said f (x)=3cos^-1(x-1)-x
And I set f (x)=0 then put the values in?
Original post by Super199
I've done it now but I swear that doesn't help does it?
I said f (x)=3cos^-1(x-1)-x
And I set f (x)=0 then put the values in?

That's one way to do it, yes. You should get a change of sign.

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