What is true about the flat rotation curves observed in spiral galaxies? 1. The astronomers were wrong--galaxy rotation curves actually decrease with distance.
2. They imply that mass exists beyond the visible edge of galaxies.
3. Supermassive black holes are much more massive than previously thought.
4. Only the Milky Way has a flat rotation curve.

To solve this system of equations by elimination, what operation could be used to eliminate the y-variable and find the value of x? 6x + 5y = 2 4x + 2y = 8 a) subtract 2 times the second equation from 3 times the first equation b) subtract 3 times the second equation from 2 times the first equation c) subtract 5 times the second equation from 2 times the first equation d) subtract 2 times the second equation from 5 times the first equation