Đáp án:
`e, C = (-1)/4`
`d, D = 1/5 + 1/(4^{99}.5)`
Giải thích các bước giải:
`e,`
`C = (1/5 - 1/7 - 1/13)/(2/5 - 2/7 - 2/13) - (3/4 - 3/16 - 3/64)/(1 - 1/4-1/16)`
`->C = (1/5 - 1/7 - 1/13)/(2 (1/5 - 1/7 - 1/13) ) - (3/4 - 3/16 - 3/64)/(4/4 - 4/16 - 4/64)`
`-> C = 1/2 - (3 (1/4 - 1/16 - 1/64) )/(4 (1/4 - 1/16 - 1/64) )`
`-> C = 1/2 - 3/4`
`-> C = 2/4 - 3/4`
`->C=(-1)/4`
Vậy `C=(-1)/4`
`d,`
`D =1/4 - 1/4^2 +... - 1/4^{98} + 1/4^{99}`
`-> 4D = 4 (1/4 - 1/4^2 + ... - 1/4^{98} + 1/4^{99})`
`-> 4D = 1 -1/4 + ... - 1/4^{97} + 1/4^{98}`
`-> 4D + D = (1 -1/4 + ... - 1/4^{97} + 1/4^{98}) + (1/4 - 1/4^2 +... - 1/4^{98} + 1/4^{99})`
`-> 5D = 1 + 1/4^{99}`
`-> D = (1+1/4^{99}) : 5`
`-> D = 1 . 1/5 + 1/4^{99} . 1/5`
`-> D = 1/5 + 1/(4^{99}.5)`
Vậy `D = 1/5 + 1/(4^{99}.5)`
