1 楼: 瞑粼
|→a + →b|^2=→a^2+→b^2+2→a·→b=|→a|^2+|→b|^2+2→a·→b=4+25-2*3=23|→a + →b|=√23|→a - →b|^2=→a^2+→b^2-2→a·→b=|→a|^2+|→b|^2-2→a·→b=4+25+2*3=35|→a + →b|=√35
2 楼: 346281401
-23