What is the equation for how many hand shakes there will be if 20 people have to shake everyone's hand?

Which expression is equivalent to sq-80

11. minitab software was used to find the lsrl for a study between x=age and y=days after arthroscopic shoulder surgery until an athlete could return to their sport. use the output to determine the prediction model and correlation between these two variables. predictor coef se coef t p constant -5.054 4.355 -1.16 0.279 age 0.2715 0.1427 1.9 0.094 r-sq = 31.16%

Which of the following expressions is equal to 2x^2+8