Tìm x , biết
( làm đầy đủ nhé )
e) 4(x-1)(x+5) – (x + 2) ( x + 5 ) = 3(x – 1 )( x + 2 )
g) ( 3x – 3 ) ( 5 + 21x ) – ( 7x + 4 ) ( 9x – 5 ) = 44
h) ( x + 1 ) ( x + 2 ) ( x + 5 ) – x^2(x + 8 ) = 27
i) 6x( 5x + 3 ) + 3x(1 – 10x ) = 7
#Làm sai = báo cáo
Đáp án:
e) x = 4
g) x = – 39/49
h) x = 1
i) x = 1/3
Giải thích các bước giải:
e) 4(x -1)(x +5) – (x + 2)(x +5) =
3(x – 1)(x + 2)
<=> 4(x² + 4x – 5) – (x² + 7x + 10) = 3(x² + x – 2)
<=> 4x² + 16x – 20 – x² – 7x – 10 = 3x² + 3x – 6
<=> 3x² + 9x – 30 – 3x² – 3x + 6 = 0
<=> 6x – 24 = 0
<=> 6x = 24
<=> x = 4
Vậy x = 4
g)(3x -3)(5 +21x) – (7x +4)(9x – 5)
= 44
<=> 63x² – 48x – 15 –
(63x² +x – 20) = 44
<=> 63x² – 48x – 15 – 63x² – x + 20 – 44 = 0
<=> – 49x – 39 = 0
<=> – 49x = 39
<=> x = -39/49
Vậy x = – 39/49
h) (x + 1)(x + 2)(x + 5) – x² ( x + 8)
= 27
<=> (x² + 3x + 2)(x + 5) – x³ – 8x² = 27
<=> x³ + 8x² + 17x + 10 – x³ – 8x² – 27 = 0
<=> 17x – 17 = 0
<=> 17x = 17
<=> x = 1
Vậy x = 1
I) 6x ( 5x + 3) + 3x ( 1 – 10x) = 7
<=> 30x² + 18x + 3x – 30x² = 7
<=> 21x = 7
<=> x = 1/3
Vậy x = 1/3
e) 4(x -1)(x +5) – (x + 2)(x +5) =3(x – 1)(x + 2)
⇒ 4(x² + 4x – 5) – (x² + 7x + 10) = 3(x² + x – 2)
⇒ 4x² + 16x – 20 – x² – 7x – 10 = 3x² + 3x – 6
⇒ 3x² + 9x – 30 – 3x² – 3x + 6 = 0
⇒ 6x – 24 = 0
⇒ 6x = 24
⇒ x = 4
g)(3x -3)(5 +21x) – (7x +4)(9x – 5)= 44
⇒ 63x² – 48x – 15 -(63x² +x – 20) = 44
⇒ 63x² – 48x – 15 – 63x² – x + 20 – 44 = 0
⇒ – 49x – 39 = 0
⇒ – 49x = 39
⇒ x = -39/49
h) (x + 1)(x + 2)(x + 5) – x² ( x + 8) = 27
⇒ (x² + 3x + 2)(x + 5) – x³ – 8x² = 27
⇒ x³ + 8x² + 17x + 10 – x³ – 8x² – 27 = 0
⇒ 17x – 17 = 0
⇒ 17x = 17
⇒ x = 1
i) 6x ( 5x + 3) + 3x ( 1 – 10x) = 7
⇒ 30x² + 18x + 3x – 30x² = 7
⇒ 21x = 7
⇒ x = 1/3
#chúc bạn học tốt!!!
OwO~