Prove that if (a, b) and (c, d) are two distinct points, the line joining them is perpendicular to the line joining (b, c) and (d, a)

How many days was the temperature above 90 degrees?

Is the response to the survey question "did you smoke in the last week question mark "response to the survey question "did you smoke in the last week? " a discrete random variable, a continuous random variable, or not a random variable?

Six random samples were taken each year for three years. the table shows the inferred population for each type of fish for each year.