Luas permukaan limas T.ABCD ialah . . . .
Pembahasan:
Panjang AB = 40 cm, BC = 16 cm, dan OT = 15 cm.
OE = BC = 16 = 8 cm,
2 2
OF = AB = 40 = 20 cm.
2 2
TE = √OT² + OE²
= √15² + 8²
= √225 + 64
= √289
= 17 cm
TF = √OT² + OF²
= √15² + 20²
= √225 + 400
= √625
= 25 cm
Luas permukaan limas T.ABCD
= LABCD + (2L∆TAB) × (2 × L∆TBC)
= (AB × BC) + (2 × ½.AB.TE) + (2 × ½.BC.TF)
= (40 × 16) + (AB × TE) + (BC × TF)
= 640 + (40 × 17) + (16 × 25)
= 640 + 680 + 400
= 1.720 cm²