<span>ABCD - трапеция </span>
<span>BK и CN - высоты из В и С на AD. </span>
<span>AD = 18 cм. </span>
<span>AB = CD </span>
<span>L A = L D = 60 град. </span>
<span>Пусть AK = ND = x </span>
<span>AB = AK / cos 60 = 2AK = 2x </span>
<span>CD = ND / cos 60 = 2ND = 2x </span>
<span>KN = BC </span>
<span>AD = AK + KN + ND = 2x + KN = 2x + BC = 18 </span>
<span>AD + BC = AB + CD </span>
<span>(2x + BC) + BC = 2x + 2x </span>
<span>2BC = 2x </span>
<span>{BC = x = </span>
<span>{2x + BC = 18 </span>
<span>2x + x = 18 </span>
<span>3x = 18 </span>
<span>x = 6 => </span>
<span>AB = 2x = 2*6 = 12 см </span>
<span>AK = x = 6 => </span>
<span>BK^2 = AB^2 - AK^2 = 12^2 - 6^2 = 108 = (10,4)^2 </span>
<span>BK = 10,4 см - высота трапеции, она де диаметр вписанной окружности. </span>
<span>S = пD^2 /4 = 3,14 * 10,4^2 / 4 = 84,78 см^2</span>
<span>ты проверь на всякий случай ( я часто ошибаюсь))))))))))))</span>