x＋y=3,xy=1,则-5x-5y＋3xy的值 a-12 b-14 c12 d18

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x＋y=3,xy=1,则-5x-5y＋3xy的值a-12b-14c12d18x＋y=3,xy=1,则-5x-5y＋3xy的值a-12b-14c12d18x＋y=3,xy=1,则-5x-5y＋3xy的值

x＋y=3,xy=1,则-5x-5y＋3xy的值 a-12 b-14 c12 d18
x＋y=3,xy=1,则-5x-5y＋3xy的值 a-12 b-14 c12 d18

x＋y=3,xy=1,则-5x-5y＋3xy的值 a-12 b-14 c12 d18
解
x+y=3
xy=1
∴-5x-5y+3xy
=-5(x+y)+3xy
=-5×3+3×1
=-15+3
=-12
选A

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