How is this formula ( Rt= r1 x r2 / r1 + r2) which is used to calculate total resistance of two parallel resistors found from the formula 1/R1 = 1/r1 +1/r2 ?

Física: un futbolista patea hacia el arco con una velocidad de 15m/ah, calcular: a)el alcance para un ángulo de tiro de 25º, b) el tiempo que el balón permanece en el aire.

Could we see a galaxy that is 20 billion light-years away?

When a lead acid car battery is recharged by the alternator, it acts essentially as an electrolytic cell in which solid lead(ii) sulfate is reduced to lead at the cathode and oxidized to solid lead(ii) oxide at the anode. suppose a current of is fed into a car battery for seconds. calculate the mass of lead deposited on the cathode of the battery.