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Use a special right triangle to express the cosine of 45 degree as a fraction and as a decimal to the nearest hundredth

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The special triangle you need is a right isosceles triangle, with legs 1 and hypotenuse
√(2).

As for every right triangle, you can find of the cosine of an angle using the "adjacent/hypotenuse" ratio.

In this case, the two base angles are equal, and so are the two legs. So, it doesn't matter which angle or leg you'll choose, the ratio will be


\cos(45)=(1)/(√(2))

which indeed is both the sine and cosine of 45°

Its approximated value is 0.707...

User Parampal Pooni
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