tentukan nilai k jika a). 3+4+5 + .... + k = 180 b). 3+5+7 + .... + (2k+1) = 663

Sn=n/2(2×3+(n-1)1)
180=n/2(6+1n-1)
180=n/2(1n+5)
180×n/2=1n+5
90n=1n+5
90n-1n=5
89n=5
n=89/5=17,8



2k+1=663
2k=663-1
K=662:2
k=331