1ã(a-2b)·(3a-b)
=3a²+2b²-7ab
=3|a|²+2|b|²-7|a||b|cos<aï¼b>
=3*3²+2*4²-7*3*4cos(3Ï/4)
=27+32+42â2
=59+42â2
(a+b)²
=a²+b²+2ab
=|a|²+|b|²+2|a||b|cos<aï¼b>
=3²+4²+2*3*4cos(3Ï/4)
=9+16-12â2
=25-12â2
2ãa+2b
=(1,-2)+2(-3,4)
=(1,-2)+(-6,8)
=(-5,6)
ï¼a+2b)*c
=(-5,6)*(3,2)
=-5*3+6*2
=-15+12
=-3
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追ç(3a-2b)·(a-2b)
=3a²+4b²-8ab
=3|a|²+4|b|²-8|a||b|cos
=3*3²+4*4²-8*3*4cos(3Ï/4)
=27+64+48â2
=91+48â2