Solution
= Solution
The constant from part (i) is found by setting $x=0$:
$$
F(0)=s(a).
$$
Taking $a=x+y$ therefore gives the <sine addition formula>
$$
\boxed{s(x+y)=s(x)c(y)+c(x)s(y)}.
$$
= Solution
The constant from part (i) is found by setting $x=0$:
$$
F(0)=s(a).
$$
Taking $a=x+y$ therefore gives the <sine addition formula>
$$
\boxed{s(x+y)=s(x)c(y)+c(x)s(y)}.
$$