Втреугольнике авс из вершины прямого угла в проведен перпендикуляр вк к стороне ас. ав=15 см, вс=20 см. из вершины в к плоскости треугольника авс проведен перпендикуляр вd. найдите расстояние от точки d до гипотенузы ас, если bd=16 см решать нужно с теоремы о трех перпендикулярах)

из вершины прямого угла в проведен перпендикуляр вк к стороне ас. -это высота   h

h=bk

по теореме пифагора   гипотенуза 

ac^2=ab^2+bc^2 = 15^2+20^2=625

ac = 25 см

есть две формулы площади

s=1/2*ab*bc

s=1/2*bk*ac

приравняем s

1/2*ab*bc =1/2*bk*ac

bk =  ab*bc /ac = 15*20 / 25 =12 

имеем точку d   вне плоскости

bk - перпендикуляр к прямой ас (по условию)

bd - перпендикуляр   к плоскости (по условию), а значит перпендикуляр к ас

соединим точки к и d - получим отрезок dk - это наклонная к плоскости с проекцией вк

по теореме о трех перпендикулярах - dk тоже перпендикуляр к ас

а раз это перпендикуляр - значит кратчайшее расстояние от т. d  до гипотенузы ас

ну все -треугольник dbk - прямоугольный   - угол < dbk =90

тогда по теорме пифагора  

dk^2 = bd^2+bk^2 = 16^2+12^2=400

dk = 20 см

ответ 20 см

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ответ:   a║b.

Объяснение:

"Определите параллельны ли прямые а и б если угол пять равен 126 градусов и угол 4 / угол 2 = 7 / 3.​"

***

При пересечении двух прямых третьей образуется 8 углов:

Смежные, сумма которых равна 180° и равные вертикальные углы.

∠4:∠2=7:3. смежные углы.

Пусть ∠4=7х, а ∠2= 3х.  ∠4+∠2=180°.

7х+3х=180°;

10x=180°;

x=18°;

∠4=7x=7*18=126°;

∠2=3x=3*18=54°.

При параллельных прямых ∠5=126°  должен быть равен ∠4, как накрест лежащие  при a║b  и секущей с.

∠4=126° следовательно прямые a и b параллельны.