Answer
`1) x^2 - 9y^2 + 6y - 1`
`= x^2 - (9y^2 - 6y + 1)`
`= x^2 - (3y - 1)^2`
`= (x - 3y + 1) . (x + 3y - 1)`
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`2) P = 2/{x - 2} + 1/{x + 2} + {6 + 5x}/{4 - x^2}` `(Đk: x \ne 2 ; x \ne - 2)`
`P = 2/{x - 2} + 1/{x + 2} - {6 + 5x}/{x^2 - 4}`
`P = 2/{x - 2} + 1/{x + 2} - {6 + 5x}/{x^2 - 2^2}`
`P = {2 . (x + 2)}/{(x - 2) . (x + 2)} + {1 . (x - 2)}/{(x - 2) . (x + 2)} - {6 + 5x}/{(x - 2) . (x + 2)}`
`P = {2x + 4}/{(x - 2) . (x + 2)} + {x - 2}/{(x - 2) . (x + 2)} - {6 + 5x}/{(x - 2) . (x + 2)}`
`P = {2x + 4 + x - 2 - 6 - 5x}/{(x - 2) . (x + 2)}`
`P = {-2x - 4}/{(x - 2) . (x + 2)}`
`P = {-2 . (x + 2)}/{(x - 2) . (x + 2)}`
`P = {-2}/{x - 2}`
Vậy `P = {-2}/{x - 2}.`
