The idea is that we multiply the x coordinates together, and the y coordinates together separately. Afterward you add the products. The result of any dot product is a scalar value, aka a single number.
The dot product is useful in many applications. One of which is to determine if two vectors are orthogonal.
-51/5 and √64 are rational, the rest are irrational
Irrational numbers are numbers that never end; 9.68, line of the 8 means the number would be 9.6888888888... going on forever, meaning its irrational. 2.010010001... goes on forever, and the square root of 6 also goes on forever.
-51/5, however, does not go on forever. The square root of 64 is 8, so these two are rational.