abs() function computes the absolute value of x, while sqrt() functions computes the square root of x. the only parameter for these functions is x , which is the value to compute. abs ( 10 ) ## [1] 10 abs ( - 10 ) ## [1] 10 sqrt ( 10 ) ## [1] 3.162278 sqrt ( - 10 ) ## Warning in sqrt(-10): NaNs produced ## [1] NaN sqrt ( abs ( - 10 ) ) ## [1] 3.162278 plot ( 15 : - 15 , sqrt ( abs ( 15 : - 15 ) ) , col = "orange" ) lines ( spline ( 15 : - 15 , sqrt ( abs ( 15 : - 15 ) ) ) , col = "gold" )