Answer: a + 4
explanation: sum means what comes from two numbers being added. so you just need to add a and 4
Height of the pentagon = 9 ft
Edge of base = 3 ft

s is the length of any side = 3
n is the number of sides = 5
tan is the tangent function calculated in degrees

Volume of the pentagon = area of base (height )
Volume of the pentagon = 15.4852 (9)
Volume of the pentagon = 139.366
Volume of the pentagon = 139.37 cu.ft
The fact that the coefficients are pairwise identical (except for sign) tells you that x^2 -1 is a factor (and x-5 is the other factor). Of course, you recognize x^2-1 as a special form (the difference of squares) that is factored as (x +1)(x -1).
The zeros are x = -1, +1, +5.
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A graphing calculator confirms this.