Use Previous Answers and Recycle the Last Entry
On the TI83 Plus graphing calculator, you can use the previous answer in the next arithmetic expression you want to evaluate. If that answer is to appear at the beginning of the arithmetic expression, first key in the operation that is to appear after the answer. The calculator displays Ans followed by the operation. Then key in the rest of the arithmetic expression and press [ENTER] to evaluate it.
If you want to embed the last answer in the next arithmetic expression, key in the beginning of the expression to the point where you want to insert the previous answer. Then press [2nd][()] to key in the last answer. Finally, key in the rest of the expression and press [ENTER] to evaluate it.
If you want to reuse the last command, function, or expression entered in the calculator — but with different instructions, arguments, or variables — you can simply recall that command, function, or expression and then edit it. To do so, follow these steps:

Enter the command, function, or expression on the Home screen and then press [ENTER] to execute command or evaluate the function.
This is illustrated in the first picture.

Press [2nd][ENTER] to paste a copy of that command or function on the home screen.
This procedure is shown in the second picture.

Edit the command, function, or expression and then press [ENTER] to reevaluate it.
The third picture shows this procedure.