no 15 tolong dikerjakan , makasih

jawab

15.
T tengah HF = titik potong EG danHF
P titik potong AC danBD
maka
TP tinggi kubus  = 9

ΔCGT siku siku di G
CD = 9
GT = 1/2 diagonal = 9/2 √2
CT = √(CG²+ GT²) = √(9 )²+ (9/2√2)² = √243/2 = 4√6

AC = diagonal sisi = 9√2

titik Q pada CT sehingga AT tegak lurus CT
AT =  jarak A ke CT

Luas  ACT = 1/2 (AC)(TP) = 1/2 (AT)(CT)
AC . TP = AT. CT

AT = AC. TP / CT
AT =  (9√2)(9) / (4√6)
AT = 81√2/ 4√6
AT = 27/4  √3