B blakwidow Banned Joined Apr 17, 2007 Messages 48 Gender Male HSC 2007 May 19, 2007 #1 FOr the ellipse x^2/16 + y^2/9 = 1 find e coordinates of foci eqn of directrix parametric eq.
P pLuvia Guest May 19, 2007 #2 If I remember correctly b2=a2(1-e2) Sub in b and a then solve for e Spoiler e=sqrt(7)/4 Foci: (+ae,0) Spoiler (+sqrt(7),0) Directrix: x=+a/e Spoiler x=+16/sqrt(7) Parametric equation: (acos@, bsin@) Spoiler (4cos@, 3sin@) Last edited by a moderator: May 20, 2007
If I remember correctly b2=a2(1-e2) Sub in b and a then solve for e Spoiler e=sqrt(7)/4 Foci: (+ae,0) Spoiler (+sqrt(7),0) Directrix: x=+a/e Spoiler x=+16/sqrt(7) Parametric equation: (acos@, bsin@) Spoiler (4cos@, 3sin@)
B bos1234 Member Joined Oct 9, 2006 Messages 491 Gender Male HSC 2007 May 20, 2007 #3 how did you get the last answer?? acos@ , bsin@ a=4,b=3 4cos@,3sin@ ??
D denoz Member Joined Oct 4, 2006 Messages 48 Gender Male HSC 2007 May 20, 2007 #4 yeah i thought it would be 4cos@, 3sin@ as well because isn't @ just -pi <@< pi
B bos1234 Member Joined Oct 9, 2006 Messages 491 Gender Male HSC 2007 May 20, 2007 #6 If P(acos@,bsin@) lies on an ellipse and M the directrix has eqn x=a/e and S(ae,0) is focus then PS = ePM PS =e(a/e - acos@) simplifying, a(1-ecos@) how does S'P = a(1+cos@)
If P(acos@,bsin@) lies on an ellipse and M the directrix has eqn x=a/e and S(ae,0) is focus then PS = ePM PS =e(a/e - acos@) simplifying, a(1-ecos@) how does S'P = a(1+cos@)
P pLuvia Guest May 21, 2007 #7 PS'=ePM' =e(acos@+a/e) =a(ecos@+1) Since the distance from PM' is acos@+a/e
