1.

Find the values of the following trigonometric ratios:cos \(\cfrac{19\pi}4\)

Answer»

Given cos \(\cfrac{19\pi}4\)

⇒  cos \(\cfrac{19\pi}4\) = cos 855°

⇒ 855° = 90° × 9 + 45°

855° lies in the second quadrant in which the cosine function is negative.

∴ cos 855° = cos (90° × 9 + 45°)

= -sin 45°

\(\cfrac{-1}{\sqrt2}\)



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