when i entered the first line,why always show the second line. i need to release hold it ,can anyone tell me what's wrong
It's hard to tell what is causing this.
Try saving your work. Then quit the kernel by evaluating the command "Quit". Then try entering the formula in a fresh notebook. It should work fine then.
What is the actual input (by which I mean something I can cut and paste rather than an image)? Probably you have something already defined and maybe there is a warning message that is not shown above?