kubus PQRSTUVW,Luas bidang QST=24 akar 3,hitung :
a.panjang rusuk kubus
b.panjang diagonal sisi
c.panjang diagonal ruang
d.volumenya
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PR=QS =ST=QT = a√2, QX = SX = (1/2)√2 satuan
Dari Δ SAT gunakan Pythagoras
XT^2 = ST² – SX²
= (a√2)² – ((1/2)a√2)²
= 2a² – (1/2)a²
= (3/2)a²
XT = V(3/2)a²
= (1/2)a√6 satuan
Luas QST = (1/2)QS(XT)
24√3 = (1/2)(a√2)(1/2)(a√6)
= (1/4)(a²√12)
24V3 = (1/2)a²2√3
(1/2)a² = 24
a² = 48
a = V48
a = 4√3 satuan
a) Panjang rusuk a = 4√3 satuan
b) Diagonal sisi aV2 = 4√3(√2)
= 4√6 satuan
c) Diagonal ruang a√3 = 4√3(√3) = 4(3) = 12 satuan
d) Volume Kubus a^3 = (4√3)³ = 576√3 satuan