b1

bai tren sai

b2

b3

b3

b3

B4

1
a. √(4 + 2√3) - √(4 - 2√3)
= √(3 + 2√3 + 1) - √(3 - 2√3 + 1)
= √[(√3 + 1)^2] - √[(√3 - 1)^2]
= |√3 + 1| - |√3 - 1|
= √3 + 1 - (√3 - 1)
= √3 + 1 - √3 + 1
= 2
b. [1/(√5 - √2) - 1/(√5 + √2) + 1] * 1/(√2 + 1)^2
= [√5 + √2 - (√5 - √2) + (√5)^2 - (√2)^2]/[(√5)^2 - (√2)^2]] * 1/(√2+1)^2
= (√5 + √2 - √5 + √2 + 5 - 2)/(5 - 2) * 1/(√2 + 1)^2
= (2√2 + 3)/3 * 1/(√2 + 1)^2
= (2√2 + 3)/3(√2 + 1)^2

3a
ĐKXĐ : x khác 3 và x > 0
D = [(x + 3)/(x - 9) + 1/(√x + 3)] : √x/(√x - 3)
    = (x + 3 + √x - 3)/(x - 9) : √x/(√x - 3)
    = (x + √x)/(x - 9) * (√x - 3)/√x
    = √x(√x + 1)/(√x - 3)(√x + 3) * (√x - 3)/√x
    = (√x + 1)/(√x + 3)

4a
E = [(x + 2)/(x√x + 1) - 1/(√x + 1)] * 4√x/3 (với x > 0)
   = {(x + 2)/[(√x)^3 + 1)] - 1/(√x + 1)} * 4√x/3
   = [x + 2 - (x - √x + 1)]/(x√x + 1) * 4√x/3
   = (x + 2 - x + √x - 1)/(x√x + 1) * 4√x/3
   = (√x + 1)/(x√x + 1) * 4√x/3
   = (√x + 1)/(√x + 1)(x - √x + 1) * 4√3/3
   = 4√3/3(x - √x + 1)