P=(x−x+1x+2):bigg(x+1x−1−xx−4)(x≥0;x̸=1;x̸=4)
P=x+1x(x+1)−x−2:(x+1x−(x+1)(x−1)4−x
P= x+1x+x−x−2:(x+1)(x−1)x(x−1)−4+x
P=x +1x−2:(x+1)(x−1)x−x−4+x
P=x+1x−2.x−4(x+1)(x−1)
P=(x−2).(x+2)(x−2)x−1
P=x+2x−1
b) P=x+2x−1=x+2x+2−3=1−x+23
Vì x≥0∀x
nên x+2≥2∀x
⇒ x+23≤23
⇒ 1−x+23≥1−23
hay P≥2−1
Dấu "=" xảy ra ⇔ x=0⇔x=0(T/m)
Vậy Pmin=2−1⇔x=0