C-09-Q158mediumsingle_mcqcos90∘=?\cos 90^\circ = ?cos90∘=?a000b111c∞\infty∞dundefinedব্যাখ্যাAt 90∘90^\circ90∘ the adjacent side shrinks to zero, so cos90∘=0hyp=0\cos 90^\circ=\dfrac{0}{\text{hyp}}=0cos90∘=hyp0=0.