In IB HL grade 11 we are currently considering complex numbers. This is chapter 15 of the HL textbook that all students have.
Main concepts are argand plane, modulus, argument, polar form, euler form, cartesian form, desmoivre's theorem.
In Grade 9 SL we are currently studying the binomial theorem. This is chapter 8 of the SL textbook that all students have.
Main concepts are index laws, geometric and arithmetic sums, expansion, pascal's triangle.