Last weekend we had a birthday for our classmate Zhang Xiaohui. She is younger than me, but I am shorter than her. And she looks stronger. Of course she is heavier than me. We went to a shop to buy a present for Xiaohui. What did we buy? We bought a doll for her. Because she told me " I haven't got a lovely doll." When she got our present she looked excited. She was very happy. We went to the zoo. We saw elephants. We wanted to row a boat in Jingming park, but it was later, we had to went home. We had a good time on that day.

（1）先化简，再求值：（2a²﹣5a）﹣2（3a﹣5+a²）．其中a=﹣1；
（2）若|m|=4，|n|=3，且知m＜n，求代数式m²+2mn+n²的值．