已知X1*X2=1 ,X1+X2=3 ,求X1三次方+X2三次方

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已知X1*X2=1 ,X1+X2=3 ,求X1三次方+X2三次方
已知X1*X2=1 ,X1+X2=3 ,求X1三次方+X2三次方

已知X1*X2=1 ,X1+X2=3 ,求X1三次方+X2三次方
x1³ + x2³
= (x1 + x2)(x1² - x1*x2 + x2²)
= (x1 + x2)[(x1 + x2)² - 3x1*x2]
= 3×(3² - 3×1)
= 3×6
= 18

x1*x2=1;x1+x2=3
x1^3+x2^3=(x1+x2)(x1^2-x1*x2+x2^2)
=(x1+x2)[(x1+x2)^2-3x1*x2]
=3*(3^2-3*1)
=18
X1三次方+X2三次方
=18