题目内容
已知a+b=3,ab=-2,求各式的值:
①a2+b2
②a3b+ab3
①a2+b2
②a3b+ab3
(1)∵a+b=3,
∴(a+b)2=9,
∴a2+b2+2ab=9,
又∵ab=-2,
∴a2+b2,
=9-2ab,
=9+4,
=13,
(2)a3b+ab3,
=ab(a2+b2),
=(-2)×13,
=-26.
∴(a+b)2=9,
∴a2+b2+2ab=9,
又∵ab=-2,
∴a2+b2,
=9-2ab,
=9+4,
=13,
(2)a3b+ab3,
=ab(a2+b2),
=(-2)×13,
=-26.
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