FORMULA, a theorem or general rule, or expression, for solving certain particular cases of some problem, &c.

so \frac{1}{2}s + \frac{1}{2}d is a general formula for the greater of

(A) The hours of the Chinese are double ours: the hour yn begins at three in the morning, and ends at five; ouei begins at three in the afternoon and ends at five.

Formula two quantities whose sum is s, and difference d; and
\frac{1}{2}s - \frac{1}{2}d is the formula, or general value, for the less
quantity. Also \sqrt{dx-x^2}, is the formula, or general
value, of the ordinate to a circle, whose diameter is d,
and absciss x.