10.1 3) z₁ = -8 - 7i; z₂ = -3i
z₁ + z₂ = -8 - 7i - 3i = -8 - 10i
z₁z₂ = -3i(-8 - 7i) = -3i·(-8) - 3i·(-7i) = 24i + 21i² = 24i - 21
4) z₁ = 5 + √3i; z₂ = 5 - √3i
z₁ + z₂ = 5 + √3i + 5 - √3i = 10
z₁z₂ = (5 + √3i)(5 - √3i) = 25 - 5·√3i + 5·√3i - 3i² = 25 + 3 = 28
i² = -1