diketahui deret geometri tak hingga r = -2/3 s~ = -12 ditanya a....?

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

a = S∞ / (1 - r)
a = (-12) / (3/3 - (-2/3))
a = (-12) / (5/4)
a = (-12) . 4/5
a = -48/5
a = -9 3/5