ince there is no reason why OP should everchange sign. Hence sin A is positive when A is between 0° and 180°,negative when between 180° and 360°. ONCos A = ——, and has therefore the same sign as ON. Hence cos A is positive when A is between 0° and 90°,negative when between 90° and 270°, and… … TRIGONOMETRICAL FUNCTIONS OF AN ANGLE. 117 between 180° and 270°; negative when it is between 90° and180°, or between 270° and 360°. OP Sec A = ——, and has therefore the same sign as cos A. In like manner may be determined the signs of cot .4 andcosec A. Vers A is always positive. The sign of chd A…
![An illustration from Divina proportione : opera a tutti glingegni perspicaci e curiosi necessaria oue ciascun studioso di philosophia: prospettiua pictura sculptura: architectura: musica: e altre mathematice: suavissima: sotile: e admirabile doctrina consequira: e delecterassi: co[n] varie questione de secretissima scientia (1509)](https://img.insideoutlibrary.com/img/200/ia-divinaproportion00paci-86-129.webp)
