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Math·Geometry and Trigonometry·Right triangles and trigonometry

easy

In right triangle $RST$, the sum of the measures of angle $R$ and angle $S$ is $90$ degrees. The value of $\sin (R)$ is $\frac{2\sqrt{10}}{7}$.

What is the value of $\cos (S)$?

A

$\frac{3\sqrt{10}}{20}$

B

$\frac{2\sqrt{10}}{7}$

C

$\frac{7\sqrt{10}}{20}$

D

$\frac{2\sqrt{10}}{3}$