Misalkan u1,u2,u3,u4,u5 adalah lima suku pertama deret geometri. Jika log u1 + log u2 + log u3 + log u4 + log u5 = 5 log 3, maka u3 = ...... a. 5 b. 4 c. 3 d. 2

u1, u2, u3, u4, u5==»
a, ar, ar^2, ar^3, ar^4
log u1 + log u2 + log u3 + log u4 + log u5
= log (u1.u2.u3.u4.u5)
= log ( a x ar x ar^2 x ar^3 x ar^4 )
= log ( a^5.r^10 )
= log ( a.r^2)^5
= 5. log ( a.r^2) = 5log 3
= a.r^2 = 3
u3 = 3. ( C )