1.

If x^2+y^2=13 and xy=6,find x^3+y^3

Answer»

X^2+y^2=(x+y)^2-2xy
xy=6
x^2+y^2=13
13=(x+y)^2-2×6
13-12=(x+y)^2
√1=x+y
1=x+y
x^3+y^3=(x+y)^3-3xy(x+y)
x^3+y^3=1^3-3×6×1
=1-18=-17


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