Question 1203116
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Consider the height of the pyramid and relate it to half of the base length.


This ratio is the tangent of the slope angle

    tan(a) = {{{H/((B/2))}}} = {{{210/((700/2))}}} = {{{210/350}}} = {{{3/5}}} = 0.6.


Hence, the slope angle is  a = arctan(0.6) = 30.96 degrees,  or about 31 degrees.
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Solved, with explanation.