Arc length of -90 degrees partial circle with radius of 1

What is the domain of the function f(x)=^9x

Create a real-life situation and create a system and show how it might be modeled algebraically with a system of equations (or inequalities) show all work include a few sentences explaining the situation, your variables of choice and what each represents, and how you would set it up and solve it algebraically. !

Two sides of a triangle mesure 20cm and 30cm. what is the measure of the third side