`text{Mình làm 4A ạ !!}`
a) P = (`frac{1}{√x + 2}` + `frac{1}{√x - 2}`).`frac{√x - 2}{√x}`
= `frac{√x - 2 + √x + 2}{(√x + 2)(√x - 2)}`.`frac{√x - 2}{√x}`
= `frac{2√x}{√x + 2}`.`frac{1}{√x}`
= `frac{2}{√x + 2}`
b) Ta có:
`frac{7P}{3}`
= 7.`frac{2}{√x + 2}` : 3
= `frac{14}{√x + 2}` : 3
= `frac{14}{3(√x + 2)}`