How to Define Product-to-Sum and Sum-to-Product Formulas
TL;DR: Got a product of two trig functions you don’t know what to do with, like sine of A times cosine of B? Product-to-sum formulas rewrite it as a sum or difference of trig functions that’s much easier to handle. Sum-to-product formulas go the other direction. Why bother? Because both transformations turn ugly trig integrals, […]
How to Add and Subtract Angles
To add or subtract angles in degrees, combine degrees with degrees and minutes with minutes, regrouping 60 minutes as 1 degree. For example, 35°40′ + 20°30′ = 55°70′ = 56°10′. In radians, add or subtract the values directly, using a common denominator for multiples of π: π/3 + π/6 = π/2. Angles, fundamental elements in […]
