# Quick C4 Question - Sin/Cos Parametic GraphWatch

#1

(i) "At E: θ = 2[Pi]"
(ii) "Max height when θ = [Pi]"

I know how to solve it from there, but where do you get 2[Pi] and [Pi] from in the first place. I think im missing something onvious.

0
9 years ago
#2
haha. I just did this question earlier. I completely blanked the first time I looked at it. Had lunch, came back, and it was much easier!
for i) notice that at both point O and E, y=0. So set the y parametric equation to 0 and solve to find theta. You'll find two values of theta that solve the equation. Plug these values into the x parametric equation to get the x coords of point O and E. O has coord 0 and E has coord 2pi.
for ii) its a lot simpler. notice that y=a(1-cost). The largest number that can come out of that bracket is 2 because cost oscillates between 1 and -1. So if the max value of the bracket is 2, then the max value of y is whats in the bracket * a, or 2a
0
#3
(Original post by ogloom)
haha. I just did this question earlier. I completely blanked the first time I looked at it. Had lunch, came back, and it was much easier!
for i) notice that at both point O and E, y=0. So set the y parametric equation to 0 and solve to find theta. You'll find two values of theta that solve the equation. Plug these values into the x parametric equation to get the x coords of point O and E. O has coord 0 and E has coord 2pi.
for ii) its a lot simpler. notice that y=a(1-cost). The largest number that can come out of that bracket is 2 because cost oscillates between 1 and -1. So if the max value of the bracket is 2, then the max value of y is whats in the bracket * a, or 2a
Thanks for the help ! C4 is such a ***** lol

I understand how to solve (ii) but I still dont get (i)

You said:
Set the y parametric equation to 0
So: a(1-cost)=0
so a = 0
and Cost = 1 ---> t = 0 ???

What am I doing wrong !!!
0
9 years ago
#4
You were good up until a(1-cost)=0.
We don't need to know a for this next step: divide both sides by a.
(1-cost)=0 (as 0/a=0)
from there cost=1 and from there t=0 and 2pi.
0
#5
(Original post by ogloom)
You were good up until a(1-cost)=0.
We don't need to know a for this next step: divide both sides by a.
(1-cost)=0 (as 0/a=0)
from there cost=1 and from there t=0 and 2pi.

ooo, yeh I got t=0, but didnt relise you use an extra solution ie 2pi (360)

Thanks mate !!
0
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