
已知a的2次方+2ab=5,ab+2b的 2次方=-2,则2a的2次方+5ab+2b的2次方=
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a^2+2ab=5
ab+2b^2=-2
2a^2+5ab+2b^2
=2a^2+4ab+ab+2b^2
=2(a^2+2ab)+(ab+2b^2)
=2*5-2
=10-2
=8
ab+2b^2=-2
2a^2+5ab+2b^2
=2a^2+4ab+ab+2b^2
=2(a^2+2ab)+(ab+2b^2)
=2*5-2
=10-2
=8
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