No 14 dong kak tolong..

diket: U3=5
U7=21
dit U12=?

jwb;
b=(U7-U3):(7-3)
=(21-5):(4)
=16:4
=4

U3=5,U2=1,U1=-3

Un=a+(n-1)b
U12=-3+(12-1)4
=-3+(13)4
=-3+52
=49


maaf kalau salah:)