1, -3, 9, -27, what is the seventh number in the sequence

This sequence can be modeled by , and that if n is even, the number becomes negative. So the seventh number would be 3^6, and that is 729, since 7 is odd.

We can use an equation to find the gravitational force exerted on the HST.
F = GMm / r² G is the gravitational constant, M is the mass of the Earth, m is the mass of the HST, r is the distance to the center of the Earth. This force, F, provides the centripetal force for the HST to move in a circle.

The equation we use for circular motion is: F = mv^2 / r, m is the mass of the HST, v is the tangential speed, r is the distance to the center of the Earth. Now we can equate these two equations to find v.

mv² / r = GMm / r² v² = GM / r v = √{GM / r } v = √{(6.67 x 10^{-11})(5.97 x 10^{24}) / 6,949,000 m} v = 7570 m/s which is equal to 7.570 km/s

HST's tangential speed is 7570 m/s or 7.570 km/s