To calculate the signal energy for a function like x(t) = rect(t) sin(2*pi*t), one must consider the voltage and current relationships over time, or the voltage and impedance involved. The energy can be computed using the formula 1/2 x^2(t) / R, assuming x(t) represents voltage across a resistor. An alternative method involves finding the limit as t approaches infinity of the integral of the square of the function over its period. Understanding these calculations is essential for accurately determining signal energy. Proper application of these principles is crucial for effective analysis in signal processing.