(2a-3b)(2a+b)=3
4a²+2ab-6ab-3b²=3;
4×4-4ab-3×9=3;
4ab=-14;
ab=-7/2;
|a+b|=√（a+b）²=√(a²+b²+2ab)=√(4+9-7)=√6;谢啦满意请采纳。嗯嗯