Question

The sum of infinite series of a GP is 4 & the sum of cubes of these terms is 192, then common ratio is-

• A. 2
• B. –2
• C. –1/2
• D. None

Answer 1

Answer: (C)

–1/2

Answer 2

\ = 4 Ž a = 4(1 – r)

& = 192 Ž $\frac { 64 ( 1 - r ) ^ { 3 } } { 1 - r ^ { 3 } }$ = 192 Ž = 3

Ž 1 + r² – 2r = 3 + 3r + 3r² Ž 2r² + 5r + 2 = 0