In functional programming, functions can be assigned to variables, passed to other functions as parameters, and returned as values from other functions. Such functions are known as First Class Functions. A higher-order function is a function which takes a function as argument or returns a function. Examples: object HOFuncs extends App { def sum(f: Int => Int, a: Int, b: Int):Int = { if (a > b) 0 else f(a)+sum(f,a+1,b) } def sq(x: Int) : Int = x*x def cube(x: Int) : Int = x*x*x def usrFun(x: Int) :Int = x + x*x println("sum(sq,1,3) = "+sum(sq,1,3)) // 1*1 + 2*2 + 3*3 = 1+4+9 = 14 println("sum(cube,1,3) = "+sum(cube,1,3)) // 1+8+27 = 36 println("sum(usrFun,1,3) = "+sum(usrFun,1,3)) // (1+1*1)+(2+2*2)+(3+3*3) = 2 + 6 + 12 = 20 } Output: sum(sq,1,3) = 14 sum(cube,1,3) = 36 sum(usrFun,1,3) = 20 Now I am going calculate integral of function of one variable with mathematics and with scala. Als...