Command 'coeff' (CAS Mode)

[hp-zl]

There is a trigonometric series (screenshot):
a:=(5*q+1)*sin(2*v)+(6*q^2+2)*sin(4*v)

We want to find the coefficient of sin(2*v), so we do:
coeff(a, sin(2*v),1) we get the correct result: 5*q+1.

But when we type:
coeff(a, sin(v*2),1) then we get zero.

With 'sin(4*v)' similarly (see screenshot).

The same results are given by both the physical calculator (with the latest firmware 2.1.14730) and the virtual calculator (HP_Prime_Virtual_Calculator-x86_64.AppImage, firmware 2.1.14288).

What do you think about it?
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