If x^2 + y^2 =58 and xy=21, find the vlaue of (x+y)^2 and (x-y)^2.

if x^2+y^2=1 and xy = 7.5 , find the value of (x^4 -y^4)

i really don't know how to start , have been thinking for the whole night, still can't do it :(

Thank you.

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- Dec 16th 2009, 04:56 PMvivienurgent help please... solving simultaneous with powers.
If x^2 + y^2 =58 and xy=21, find the vlaue of (x+y)^2 and (x-y)^2.

if x^2+y^2=1 and xy = 7.5 , find the value of (x^4 -y^4)

i really don't know how to start , have been thinking for the whole night, still can't do it :(

Thank you. - Dec 16th 2009, 05:01 PMskeeter
- Dec 16th 2009, 05:04 PMpickslides