giúp nha năn nỉ á đang cần gấp

`a) A = 1 - 4/23 + 5/21 - 4/23 + 16/21`

`A = 1 + (5/21 + 16/21) - (4/23 + 4/23)`

`A = 1 + 21/21 - 8/23`

`A = 1 + 1 - 8/23`

`A = 2 - 8/23`

`A = 38/23`

`b) B = 0,8 * sqrt(25/9) - 2/7 * sqrt(5 4/9) + (-1/2)^2 * 4^2`

`B = 4/5 * 5/3 - 2/7 * sqrt(49/9) + 1/4 * 16`

`B = 4/3 - 2/7 * 7/3 + 4`

`B = 4/3 - 2/3 + 4`

`B = 2/3 + 4`

`B = 14/3`

`c) C = (-4/13) * (5/17) + (-12/13) * (4/17) + 4/13`

`C = -20/(13*17) - 48/(13*17) + 4/13`

`C = (-20 - 48)/(13*17) + 4/13`

`C = -68/(13*17) + 4/13`

`C = -(4*17)/(13*17) + 4/13`

`C = -4/13 + 4/13`

`C = 0`