If x+y+ z = 8 and xy +yz+zx = 20 find the value of x3
+y3
+z3
-3xyz.
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Answer:
x^3+y^3+z^3-3xyz
=(x+y+z)(x^2+y^2+z^2-xy-yz-zx)
=8{(x+y+z)^2-2(xy+yz+zx)-(xy+yz+zx)}
=8{(8)^2-3(xy+yz+zx)}
=8{64-3.20}
=8{64-60)
=8.4
=32
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