Jawabanmu

2014-05-21T21:08:26+07:00
Luas Layang-Layang =  \frac{1}{2} x Diagonal x Diagonal
420 =  \frac{1}{2} x 24 x Diagonal
Diagonal =  \frac{420}{12}
Diagonal = 35cm 

Semoga Benar ^^
420 = 1/2 x 24 x D2
trus
420 = 12D2
D2 = 420 : 12 = 35 :D
;)
2014-05-21T21:14:10+07:00
L = d1 x d2 : 2

d1 = L x 2 : d2
     = 420 x 2 : 24
     = 35 cm