如图所示旁握仿,
cos<运纤AM*DN>=|AM*DN|/|AM||DN|
=(-2*2+4*2+√2*2√2)/√(2²+4²+√2²)√(2²+2²+(2√2)²皮物)
=(-4+8+4)/√22*√16
=2/√22
=√22/11