设|a|=3,|b|=2,a*b=-4,求a*(a-2b);|2a+3b|_数学解答

设|a|=3,|b|=2,a*b=-4,求a*(a-2b);|2a+3b|

人气：477 ℃　时间：2020-03-28 14:42:17

解答

解
/a/=3,/b/=2,a*b=-4
∴a(a-2b)
=a²-2ab
=9+2×4
=9+8
=17
/2a+3b/
=√(2a+3b)²
=√4a²+12ab+9b²
=√4×9-12×4+9×4
=√36-48+36
=√24
=2√6