题目

I was filled with doubts and worries until my grandfather told me to stand tall.For me, height was my trouble. I was much taller than other girls, I often bent（ 弯曲） my body at the back of the line. I had always felt unsafe as the tallest student of my class in Bala Cynwyd. And I wasn't looking forward to entering the ninth grade.My grandfather didn't laugh at me. Instead, whenever I tried to bend myself in order to appear shorter, he would tell me Stand straight and tall, Alisa. I trusted my grandfather more than anyone else in my childhood. And whenever I was afraid of something, he a已知定义域为R的函数f（x）= 是奇函数，（1）求实数a的值；（2）若对任意的t∈R，不等式f（t2﹣2t）+f（2t2﹣k）＜0恒成立，求实数k的取值范围；（3）设关于x的方程f（4x﹣b）+f（﹣2x+1）=0有实数根，求实数b的取值范围．