(2 ĐIỂM) TÌM X BIẾTA) 4X2 – 12X = -9B) (5 – 2X)(2X + 7) = 4X2 – 25 4X2...
Câu 3: (2 điểm) Tìm x biết
a) 4x
2
– 12x = -9
b) (5 – 2x)(2x + 7) = 4x
2
– 25
4x
2
– 12x + 9 = 0
(5 – 2x)(2x + 7) – (2x – 5)(2x + 5) = 0
(5 – 2x)(2x + 7 + 2x + 5) = 0
(2x – 3)
2
= 0
x = 3/2
(5 – 2x)(4x + 12) = 0
c) x
3
+ 27 + (x + 3)(x – 9) = 0
5
x
5 2
0
2
(x + 3)(x
2
– 3x + 9) + (x + 3)(x – 9) = 0
4
12 0
3
(x + 3)(x
2
– 3x + 9 + x – 9) = 0
d) 4(2x + 7)
2
– 9(x + 3)
2
= 0
(x + 3)(x
2
+ x) = 0
4(2x + 7)
2
= 9(x + 3)
2
0
x
x
2(2
7) 3(
3)
1
23
x(x + 3)(x + 1) = 0
2(2
7)
3(
3)
7
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