Final answer:
The expression (-1/2at) - (12t^3) is already in a simplified form and equivalent to option B) -0.5at - 12t^3, which corresponds to the requested Ax^my^n format, where A is the coefficient and x and y are placeholders for variables with their respective exponents.
Step-by-step explanation:
To convert the expression (-1/2at) - (12t^3) into the form Ax^my^n, we first identify the variables and their exponents in the expression. Since the expression is already simplified, we can directly write it in the form of Ax^my^n, considering that x and y are just placeholders for any variables and At, t^3 are already the given variables in the expression.
In this case, we have two terms: -1/2at and -12t^3. The variable a has an exponent of 1, and the variable t also has an exponent of 1 in the first term. In the second term, t has an exponent of 3.
Thus, the given expression is equivalent to option B) -0.5at - 12t^3.