In this problem, we are given two angles, r and r1, inside a prism with an angle of 50∘. The angle r changes with time according to the equation r=10∘+t2. To find out how r1 changes with time, we follow these steps: Since the sum of angles r and r1 inside the prism must equal the prism's angle, we write: r+r1=50∘ Substitute the expression for r into the equation: (10∘+t2)+r1=50∘ Solve for r1 : r1=50∘−10∘−t2=40∘−t2 Therefore, during the time interval considered, the angle r1 varies with time as 40∘−t2.