MATH PLEASE HELP When a radioactive substance​ decays, measurements of the amount remaining over constant intervals of time form a geometric sequence. The table shows the amount of a certain​ substance, remaining after different constant intervals. Write the explicit and recursive formulas for the geometric sequence formed by the amount of the radioactive substance remaining. The explicit formula for the geometric sequence formed by the amount of the radioactive substance remaining is a^n. ​(Type your answer using exponential​ notation.)