The sum of the squares of c and d is 25 The square of c means we we raise c to the power of 2: c^2 The square of d means we we raise d to the power of 2: d^2 The sum of the squares of c and d means we add d^2 to c^2: c^2 + d^2 The word is means equal to, so we set c^2 + d^2 equal to 25: c^2 + d^2 = 25