luas permukaan sebuah tabung dengan jari jari r dan tinggi 3 r

jari-jari = r
tinggi = 3r

L pt = (2 × phi × r^2) + (2 × phi × r × t)
L pt = 2 × phi × r × (r + t)
L pt = 2 × phi × r × (r + 3r)
L pt = 2 × phi × r × 4r
L pt = 8 × phi × r^2

L. Permukaan Tabung : 2x L.alas + L. selubung

it's means that : 2nr² + 2nrt (sorry 'cause I haven't " phi" in my keyboard). it could be practicing become 2nr (r+t), So, the point the answer is 2nr(r+3r) <=> 2nr(4r) <=> 8nr²