jumlah 5 suku pertama deret geometri adalah 242. jika rasionya -2 tentukan jumlah nilai suku ke-5 dan suku ke -7 deret tsb

S5 = 242
r = -2

S5 = a(1-r^5) / 1-r
242 = a(1-(-2)^5) / 1-(-2)
242 = a(1-(-32)) / 3
242 = a(33) /3
242 × 3 = 33a
726 = 33a
a = 22

U5 + U7
= ar^4 + ar^6
= 22×(-2)^4 + 22×(-2)^6
= 22×16 + 22×64
= 352 + 1408
= 1760

semoga membantu yaa:)

r= -2
S5 = 242

S5 = a (1-r^5)/1-r
242 = a (1 - (-2)^5/1+2
242 = a( 1+32)/3
242 x 3 = 33a
726= 33a
a = 22

U5 = ar^4
= 22(-2)^4
= 22(16)
=352

U7 = ar^6
= 22(-2)6
= 22(64)
=1408