Words to the wise: Please express exponentials as x^2, not x2.
x2 + y2 = 81 should be <span>x^2 + y^2 = 81 = 9^2 Comparing this to x^2 + y^2 = r^2, we see that r= radius=9. y-intercepts are where x=0, so purposely set x=0 and solve for y:
0^2 + y^2 = 9^2. Then y = 9 or y = -9.
The graph intersects the y-axis at (0,9) and (0, -9).</span>
Firstly, the moon keeps changing its shape with 4 distinct moon phases that depend on the position of the moon and also on the position of the Earth. The moon orbits around the planet Earth, and the Earth orbits around the Sun.
