::algebra (including finding roots of polynomials)
::algebra (including finding roots of polynomials)
::linear algebra—vector spaces, inner products, Hermitian and unitary operators, Hilbert spaces, etc.
::linear algebra—vector spaces, inner products, Hermitian and unitary operators, Hilbert spaces, etc.
+
::number theory—This seems improbable, but it is true. The Riemann zeta function, and the Riemann hypothesis, are very important in number theory. For a long time, the only proofs of the prime number theorem used complex numbers. The Wiles/Taylor proof of [[Fermat's Last Theorem]] uses modular forms, which use complex numbers.