SOLUTION: if x-y=-6 and xy=4, then find the value of x^3-y^3

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Question 763375: if x-y=-6 and xy=4, then find the value of x^3-y^3
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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if x-y=-6 and xy=4, then find the value of x^3-y^3
write it
x = y+6
replace x in the 2nd equation
y(y+6) = 4
y^2 + 6y - 4 = 0
using the quadratic formula, I got
y ~ -6.6
y ~ +.6
then
x = -.6
x = +6.6
:
using x = -.6; y = -6.6:
-.6^3 -(-6.6^3) =
-.216 + 287.496 = 287.28
:
Using x = 6.6; y = .6
287.496 - .216 = 287.28