Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 331 1 b i Solution Created 2026-10-03 Updated 2026-10-05
For a possibly unstable normal mode, ensures never vanishes, so choose one continuous branch of . Substitute into the Taylor–Goldstein equation and collect terms:Multiplication by puts its first two terms in divergence form:Multiply by the complex conjugate and apply integration by parts. Since , the boundary term vanishes and the power-transformed Taylor–Goldstein energy identity isThe weight is , not : preserving its complex phase is essential for the subsequent stability proofs.
Past exam of the mathematics course of the University of Cambridge 2020 ia Paper 1 1C iii Solution Created 2026-09-24 Updated 2026-09-29
Past exam of the mathematics course of the University of Cambridge 2020 ia Paper 1 1C iv Solution Created 2026-09-24 Updated 2026-09-29
Past exam of the mathematics course of the University of Cambridge 2021 ib Paper 4 4C Solution Created 2026-09-24 Updated 2026-10-14
The one-dimensional Time-dependent Schrödinger equation for a wavefunction in a real potential isMultiplying this equation by , multiplying its complex conjugate by , and subtracting gives the probability continuity equationIf and its first derivative decay sufficiently rapidly as , then the probability current vanishes at both ends. Integrating the continuity equation and using the fundamental theorem of calculus yieldsThis conservation of quantum probability is required by the Born rule: once a normalizable wavefunction has total probability one, its time evolution must preserve that normalization.
For the stated Gaussian wave packet, put . Sinceits squared modulus isThe Gaussian integral then giveswhich is independent of time, as required.
Past exam of the mathematics course of the University of Cambridge 2024 iii Paper 301 4 c Solution Created 2026-09-24 Updated 2026-09-25
The Dirac field Lagrangian isChoose the Majorana spinorSubstitution shows that its two chiral kinetic terms agree after integration by parts and thatThus equals twice the displayed one-Weyl-field Lagrangian, up to a total derivative.
The lower chiral component of the Dirac equation isPutting gives exactly ; the upper component is its complex conjugate.
Past exam of the mathematics course of the University of Cambridge 2024 iii Paper 305 1 i Solution Created 2026-09-24 Updated 2026-09-25
Write . Parity reverses the spatial coordinates and must exchange the two chiral Weyl spinors. One convenient choice isThe identities and exchange the two kinetic terms after . The mass bilinear maps to its complex conjugate , so the two mass terms are exchanged and the action is invariant. More generally, independent unit phases may multiply the two transformations provided .
For , the preceding change of variables and one integration by parts giveSplit the last improper integral at one and add and subtract one on . Since ,
Past exam of the mathematics course of the University of Cambridge 2025 iii Paper 129 4 a Solution Created 2026-09-24 Updated 2026-10-03
For functions on , the Gowers inner product iswhere is the complex conjugate operator. The Gowers uniformity norm isThe Gowers-Cauchy-Schwarz inequality states
Past exam of the mathematics course of the University of Cambridge 2026 iii Paper 150 2 b Solution Created 2026-09-24 Updated 2026-10-07
The symmetric form of the functional equation of the Riemann zeta function isThe complex conjugation identity and the functional equation show that every Nontrivial zero of the Riemann zeta function is accompanied by , , and .
Write , with because the triangle is nondegenerate. Let be its circumcenter. Equality of the complex modulus values gives . Equality of , after expanding the squares, givesThus the real part and imaginary part determineUsing the complex conjugate , we also haveThereforeThe nonzero denominator is exactly the nondegeneracy condition. If is real, the three distinct collinear points do not have a finite circumcenter.
The product rule gives and . On an interval avoiding , substitution and division by giveFor a constant-coefficient differential equation, the coefficient of forces . At , the remaining coefficient also vanishes. ThusThe characteristic equation of a constant-coefficient differential equation is , with complex conjugate roots of a polynomial . Its real solutions and are linearly independent. Therefore the general solution isThe constants can be chosen independently on the two sides of the singular point. The power substitution reducing a differential equation to constant coefficients here is invertible wherever .
Past exam of the mathematics course of the year 1 of the natural sciences course of the University of Cambridge 2006 Paper 1 3 a ii Solution Created 2026-10-18 Updated 2026-10-20
The quadratic formula gives . For , write this asEach root of a polynomial has modulus , since . As increases from to , the upper root traverses the upper unit semicircle from to , and the lower root traverses the lower semicircle in the opposite angular direction. At the roots coincide at ; at they coincide at . For intermediate they are complex conjugates.
Past exam of the mathematics course of the year 1 of the natural sciences course of the University of Cambridge 2008 Paper 1 12 b i Solution Created 2026-10-18 Updated 2026-10-20
Multiply numerator and denominator by the complex conjugate of . For this givesThus its real part and imaginary part are respectively
Past exam of the mathematics course of the year 1 of the natural sciences course of the University of Cambridge 2008 Paper 2 5 Solution Created 2026-10-18 Updated 2026-10-20
Multiply numerator and denominator by the complex conjugate of :Thus the real part and imaginary part are respectively
Multiply numerator and denominator by the complex conjugate :The real part and imaginary part are therefore
Multiply numerator and denominator by the complex conjugate of the denominator:Squaring gives . Thus the real part and imaginary part are
