Rectange $JKLM$ is shown below. The given side lengths are in feet. What is the cosine of $\angle{KJL}$ ?

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Cosine refers to the ratio of the adjacent side to the hypotenuse. We can obtain the hypotenuse through the pythagorean theorem:

$$a^2+b^2=c^2$$ $$9^2+7^2 = c^2$$ $$81+49 =c^2$$ $$c = \sqrt{130}$$ $$\cos{\angle{KJL}} = \boxed{\frac{9}{\sqrt{130}}}$$