You can exploit the fact that the time to charge a capacitor is inversely proportional to a constant current used to charge it.
One implementation could be a 555 in astable operation mode, except that the timing capacitor is charged by a linear voltage controlled current source instead of through the traditional resistor tied to a fixed voltage. The voltage controlling the current source is the denominator. The other voltage is the Control Voltage terminal of the 555. The output pulse from the 555 will have an ON time proportional to the Control Voltage (numerator) but inversely proportional to the voltage controlling the current source (denominator). The small OFF time will be fixed by the time it takes the 555 to discharge the capacitor. The average value of the resulting pulse train is proportional to the numerator/denominator times the amplitude of the pulse train, such as would be obtained by integrating the pulse train.
Of course, this idea only works for steady-state input voltage, so that your input sinusoids will have to be peak detected, or something.
Other inverse relationships such a freq=1/T might be useful also.