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$$ f(x)=\sum_{n=1}^\infty a_n\cos nx+b_n\sin nx\eqno(1)$$
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$$f(x)=\sum_{n=1}^\infty a_n\cos nx+b_n\sin nx\eqno\llap{(1)}$$
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$$f(x)=\sum_{n=1}^\infty a_n\cos nx+b_n\sin nx$$
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$$f(x)=\sum_{n=1}^\infty a_n\cos nx+b_n\sin nx\leqno(2)$$
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$$f(x)=\sum_{n=1}^\infty a_n\cos nx+b_n\sin nx\leqno\rlap{(2)}$$
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\noindent
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bla bla bla  bla bla bla  bla bla bla  bla bla bla
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$$f(x)=\sum_{n=1}^\infty a_n\cos nx+b_n\sin nx\eqno(1)$$
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bla bla bla  bla bla bla  bla bla bla  bla bla bla
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$$f(x)=\sum_{n=1}^\infty a_n\cos nx+b_n\sin nx\eqno\llap{(1)}$$
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$$f(x)=\sum_{n=1}^\infty a_n\cos nx+b_n\sin nx$$
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bla bla bla  bla bla bla  bla bla bla  bla bla bla
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$$f(x)=\sum_{n=1}^\infty a_n\cos nx+b_n\sin nx\leqno(2)$$
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bla bla bla  bla bla bla  bla bla bla  bla bla bla
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$$f(x)=\sum_{n=1}^\infty a_n\cos nx+b_n\sin nx\leqno\rlap{(2)}$$
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bla bla bla  bla bla bla  bla bla bla  bla bla bla
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