Parametric question (2 Viewers)

P.T.F.E · Feb 18, 2009

x=3cost
y=3sint

find the equation by eliminating t.

thanx in advanced, i think i have the correct answer its just the process i am worried about.

hermand · Feb 18, 2009

$x^{2}=9\cos ^{2}t$
$y^{2}=9\sin ^{2}t$
add to get...
$x^{2}+y^{2}=9\left (\cos ^{2}t+\sin ^{2}t \right )$
apply trig identity........
$\therefore x^{2}+y^{2}=9\left (1 \right )$
$\therefore x^{2}+y^{2}=9$

P.T.F.E · Feb 18, 2009

hermand said:
$x^{2}=3\cos ^{2}t$
$y^{2}=3\sin ^{2}t$
add to get...
$x^{2}+y^{2}=3\left (\cos ^{2}t+\sin ^{2}t \right )$
apply trig identity........
$\therefore x^{2}+y^{2}=3\left (1 \right )$
$\therefore x^{2}+y^{2}=3$

thank you but wouldn't you have to square the three as well?

tommykins · Feb 18, 2009

Yes she forogt to square the 3.

P.T.F.E · Feb 18, 2009

ok kool thats what i got just was unsure whether u could just add them, new topic we just started and that was a 'challenging' question the teacher left us with so thought there must have been a trick to it.

Aerath · Feb 18, 2009

Yeah, in parametrics there are basically 3 types of questions where they ask you to eliminate the parameter:
1. Use substitution.
2. Use an identity (just like above, sin^2 + cos^2 = 1)
3. Combination of both.

P.T.F.E · Feb 18, 2009

kool didnt know about the identity one so i guess fluked it but was pretty logical, i knew i had to rid of the trig in it, what better way then to sqare it haha.

hermand · Feb 18, 2009

P.T.F.E said:
thank you but wouldn't you have to square the three as well?

ah yes. my bad.

i've been having a great day at maths today =||. lol.

sorry about that!

Parametric question (2 Viewers)

P.T.F.E

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hermand

je t'aime.

P.T.F.E

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tommykins

i am number -e^i*pi

P.T.F.E

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Aerath

Retired

P.T.F.E

Member

hermand

je t'aime.

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