The force F of attraction between two bodies varies jointly as the weights of the two bodies and inversely as the square of the distance between them. Express this fact as a variation using c as a constant. Use M1 and M2 for the weights of the two bodies.

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anonymous · Answer

That's Newton's Law of Gravitation. Since it varies directly with M1 and M2 and inversely with the square of the distance, we have: $$ F \alpha \frac{M_1 M_2}{d^2} $$Where alpha means that Force is proportional to that. But we need a constant, known as proportionality constant, to make the equation true. So: $$ F = c \frac{M_1 M_2}{d^2} $$