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Mathematics 13 Online
OpenStudy (el_arrow):

find the limit, if it exists, or show that the limit does not exist

OpenStudy (el_arrow):

limit (x,y)--->(0,0) xy^2cosy/x^2+y^4

OpenStudy (el_arrow):

i did the y path where x=0 and i got lim (0,y)--->(0,0) cosy/y^4

OpenStudy (zarkon):

try \[y=\sqrt{x}\]

OpenStudy (el_arrow):

okay let see

OpenStudy (el_arrow):

i got (x^2*cosy)/2x^2

OpenStudy (zarkon):

yes...simplify and take the limit

OpenStudy (el_arrow):

okay i got lim y-->0 cos(0)/2 = 1/2

OpenStudy (zarkon):

and what did you get as a final answer when you let x=0

OpenStudy (el_arrow):

i got 1/0

OpenStudy (zarkon):

no

OpenStudy (el_arrow):

its wrong?

OpenStudy (el_arrow):

i made a mistake its 0

OpenStudy (zarkon):

\[\frac{xy^2\cos(y)}{x^2+y^4}\] let x=0 \[\frac{0y^2\cos(y)}{0^2+y^4}\] \[=\frac{0}{y^4}=0\] for all y not zero

OpenStudy (zarkon):

good...is 0 equal to 1/2

OpenStudy (el_arrow):

nope so its DNE

OpenStudy (zarkon):

correct

OpenStudy (el_arrow):

thank you

OpenStudy (el_arrow):

@Zarkon how did you know to use y=sqrt(x)? is there something that tells what to use?

OpenStudy (zarkon):

it made the denominator have two x's that had the same power so I could combine them...among other things

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