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Rombo di base del prisma:
lato $\small l= \dfrac{2p}{4} = \dfrac{14}{4} = 3,5\,cm;$
semi-diagonale maggiore $\small \dfrac{D}{2}= \sqrt{l^2-\left(\dfrac{d}{2}\right)^2}= \sqrt{3,5^2-\left(\dfrac{4,2}{2}\right)^2}= \sqrt{3,5^2-2,1^2} = 2,8\,cm;$
diagonale maggiore $\small D= 2×2,8 = 5,6\,cm.$
Prisma:
area di base $\small Ab= \dfrac{D×d}{2} = \dfrac{5,6×4,2}{2} = 11,76\,cm^2;$
altezza $\small h= D= 5,6\,cm;$
area laterale $\small Al= 2p×h = 14×5,6 = 78,4\,cm;$
area totale $\small At= Al+2×Ab= 78,4+2×11,76 = 78,4+23,52 = 101,92\,cm^2.$