geometry

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What is the area of a regular pentagon with a side length of 10 inches and a distance from the center to a vertex of 10 inches?
Round your answer to the nearest tenth.

  • geometry -

    Look at one of the five isosceles triangle
    each has a 72 degree angle with sides of 10 containing that angle.

    Use the cosine law to find the base of that triangle
    x^2 = 10^2 + 10^2 - 2(10)(10)cos 72
    x = ...

    Once you have that, find the area of the triangle (1/2)(10)(10sin(above angle)
    then multiply by 5

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