Simplify (7-5i)(-3+9i)-(5+6i)^2
(-21 + 63i + 15i - 45i^2) - (25 + 60i + 36i^2) = (-21 + 78i + 45) - (-11 + 60i) = 24 + 78i - 60i + 11 = 35 + 18i