Tiga bilangan barisan aritmatika. Jumlah ketiga bilangan tersebut 21 dan hasil kali nya 280. Berapakah bilangan bilangan tersebut

misalkan a, b, dan c
2×U2 = U1 + U3
2×b = a + c
2b = a + c

a + b + c = 21
a + c + b = 21
2b + b = 21
3b = 21
b = 21/3 = 7

a + c = 2b = 2(7) = 14
a = 14 - c

a × b × c = 280
a × 7 × c = 280
a × c = 280/7
a × c = 40
(14 - c)c = 40
14c - c² = 40
0 = c² - 14c + 40
c² - 14c + 40 = 0
(c - 10)(c - 4) = 0
c = 10 atau c = 4
ambil c = 10
maka a + c = 14
a = 4
b = 7
c = 10