в а). (2+3i)² = (2+3i)(2+3i) = 4 + 6i + 6i + 9i² = 4 + 12i - 9 = -5 + 12i

в б). (3-5i)² = (3-5i)(3-5i) = 9 - 15i - 15i + 25i² = 9 - 30i - 25 = -16 - 30i

в г). (5+3i)³ = (5+3i)(5+3i)(5+3i) = (5^2 + 103i + 3^2)(5 + 3i) = (25 + 30i + 9)(5 + 3i) = (34 + 30i)(5 + 3i) = 345 + 343i + 305i + 30*3i² = 170 + 102i + 150i - 90 = 80 + 252i