Final answer:
The product of (2.1 x 10^3) and (4.0 x 10^-7) is 8.4 x 10^-4, which is calculated by multiplying the coefficients and adding the exponents in scientific notation.
Step-by-step explanation:
To multiply numbers in scientific notation, multiply the coefficients and add the exponents. In this case, (2.1 x 10˄3) X (4.0 x 10˄-7) = (2.1 x 4.0) x (10˄3 x 10˄-7).
The product of the coefficients is 2.1 x 4.0 = 8.4.
The product of the exponents is 10˄3 x 10˄-7 = 10˄(3 + (-7)) = 10˄-4.
Therefore, the final answer is 8.4 x 10˄-4.