=45°,丨向量a丨=2,丨向量b丨=3,a(2a-2b)=?
问题描述:
=45°,丨向量a丨=2,丨向量b丨=3,a(2a-2b)=?
a(2a-2b)=2(a)-3a·b
=
接下去怎么计算?
答
a(2a-2b)
=2a²-3a·b
=2*2²-3*2*3*cos45°
=8-9√2