Question

tiga buah bilangan membentuk barisan aritmatika. jumlah ketiga bilangan tersebut 36 dan hasil kalinya 1.140. bilangan terbesar adalah...
A.5
B.7
C.12
D.19

(pake cara)

Answer 1

Un = a + (n - 1)b

U1 = a
U2 = a + b
U3 = a + 2b

a + a + b + a + 2b = 36
3a + 3b = 36
a + b = 12
a = 12 - b

(a)(a + b)(a + 2b) = 1140
(12 - b)(12 - b + b)(12 - b + 2b) = 1140
(12 - b)(12)(12 + b) = 1140
(144 - b²)(12) = 1140
1728 - 12b² = 1140
-12b² = 1140 - 1728
-12b² = -588
12b² = 588
b² = 588/12
b² = 49
b = √49
b = 7

a + b = 12
a + 7 = 12
a = 12 - 7
a = 5

U3 = a + 2b
= 5 + 2(7)
= 5 + 14
= 19
---> D.

Semoga membantu:)