I'm with Gauss here
"sin 2 θ is odious to me, even though Laplace made use of it; should it be feared that might become ambiguous, which would perhaps never occur... well then, let us write (sin θ) 2 , but not sin 2 θ, which by analogy should signify sin(sin θ)." -- Gauss-Schumacher correspondence, quoted in Eli Maor, Trigonometric Delights . This must be one of the worst notational choices in mathematics.