A. √X2−4−X + 2 = 0 (ĐK
Bài 3:a. { [x=x ≥x=3−519
√
x2
−4−x + 2 = 0 (đk: x2
−4≥0¿<=>√
x2
−4 = x - 2{
x2
−4=(x−2≥0x−2)2
{
x2
−4=x ≥x2
−42 x+4 {
xx ≥=22 x = 2 (tmđk)---b.√
4x+20−3√
5+x+7√
9x+45=20 (đk: x >= - 5) 2√
x+5 −3√
x+5 + 7.3 .√
x+5 = 20 20.√
5+x = 20√
5+x = 1 x = - 4 (tmđk)---c. 2√
x+1−√
x+6=1 . (đk: x >= -1) 2√
x+1 =√
x+6+1 4( x + 1) = x + 6 + 2√
x+6 + 1 4x + 4 = x +7 + 2√
x+6 3x – 3 = 2√
x+6{
(3x−3)3x−2
=43≥0x−24 {
9x2
−18xx ≥+9=41 x+24 {
9x2
−22x ≥x−15=01{ [x=x ≥x=3−519
x = 3 (tmđk)Câu 5(0.5)Cho x ≥ 0; y ≥ 0 thỏa mãn 2√
x−√
y=1. Chứng minh rằng: x + y ≥ 152√
x−1¿¿Ta có: 2√
x−√
y=1 √
y=2√
x−1 y = = 4x - 4 √
x + 1¿Do đó: x + y - 15 = x + (4x - 4 √
x + 1) - 15 =
5x - 4 √
x + 4 =
25x−20√
x+45 =
(5√
x−2)
2
5