I need help with 9.1

Martha is designing a single-player game. her manager suggests that she plan the design to incorporate future modifications. which principle of game design relates to planning for future modifications?

In excel - calculate the actual increase/decrease from first quarter to the second quarter then subtract subtract first quarter value from second quarter total then divide result by first quarter value

For positive constants a and b, the force between two atoms in a molecule is given f(r) = −a r2 + b r3 , where r > 0 is the distance between the atoms. note: a and b are upper case letters. (a) find f '(r) = (b) find the critical point for f(r). r = (c) find f ''(r) = (d) find the value of r so that f ''(r) = 0.