Bisa tolong bantu ga nomor 10&12

10.jawaban A
pembahasan:
diketahui:un:1/2.n(n+1)(n+2)
ditanya:a.U1?
b.U2?
c.U3?
d.U4?
e.U5?
jawab/
a.U1 =1/2.1(1+1)(1+2)
=1/2.(1.2.3)
=1/2.6
=3

b.U2=1/2.2(2+1)(2+2)
=1/2.(2.3.4)
=1/2.24
=12
c.U3=1/2.3(3+1)(3+2)
=1/2.(3.4.5)
=1/2.60
=30
d.U4=1/2.4(4+1)(4+2)
=1/2.(4.5.6)
=1/2.120
=60
e.U5=1/2.5(5+1)(5+2)
=1/2.(5.6.7)
=1/2.210
=105