Đáp án:
a, `A = (4^6 . 9^5 + 6^9 . 120)/(-8^4 . 3^12- 6^11)`
` =- (2^12 . 3^10 + 2^12 . 3^10 . 5)/(2^12 . 3^12 + 2^11 . 3^11)`
` = - (2^12 . 3^10 . (1 + 5))/(2^11 . 3^11.(6 + 1))`
` = -(2.6)/(3.7) = -4/7`
`B = 1/(1 - 1/(1 - 2^-1)) + 1/(1 + 1/(12^-1))`
` = 1/(1 - 1/(1 - 1/2)) + 1/(1 + 1/(1/12))`
` = 1/(1 - 2) + 1/13`
`= -1 + 1/13 = -12/13`