a) 6x(5x + 3) + 3x(1 – 10x) = 7
⇒ 30x2+18x+3x-30x2=7
⇒21x=7
⇒x=\(\dfrac{7}{21}\)
⇒x= \(\dfrac{1}{3}\)
b) (3x – 3)(5 – 21x) + (7x + 4)(9x – 5) = 44
⇒15x-63x2-15+63x + 63x2-35x+36x-20=44
⇒79x-35=44
⇒79x=44+35
⇒79x=79
⇒x=1
d) 5x(12x + 7) – 3x(20x – 5) = - 100
⇒60x2+35x-60x2+15=-100
⇒35x+15=-100
⇒35x=-100-15
⇒35x=-115
⇒x=\(\dfrac{-115}{35}\)
⇒x=\(\dfrac{-23}{7}\)
e) 0,6x(x – 0,5) – 0,3x(2x + 1,3) = 0,138
⇒0,6x2-0,3-0,6x2-0,39x=0,138
⇒-0,3-0,39x=0,138
⇒-0,39x=0,138+0,3
⇒-0,39x=0,438
⇒x= \(\dfrac{0,438}{-0,39}\)
⇒x=\(\dfrac{-73}{65}\)
a) 6x(5x+3)+3x(1-10x) = 7
6x.5x + 6x.3 + 3x.1 - 3x.10x = 7
30x² + 18x + 3x - 30x² = 7
30x² - 30x² +18x + 3x = 7
(30x² - 30x²) + (18x + 3x) = 7
21x = 7
x = 7:21
x = 1/3
Vậy x = 1/3
b) (3x−3)(5−21x) + (7x+4)(9x−5) = 44
15x − 63x2 − 15 + 63x + 63x2 − 35x + 36x − 20 = 44
79x −35 = 44
79x = 44 + 35
79x = 79
x = 79:79
x = 1
Vậy x = 1
c) (x+1)(x+2)(x+5) − x2(x + 8) = 27
x2 + 2x + x + 2(x + 5) − x3 − 8x2 = 27
x2(x + 5) + 2x(x + 5) + x(x + 5) + 2(x + 5) − x3 − 8x2 = 27
x3 + 5x2 + 2x2 + 10x + x2 + 5x + 2x + 10 − x3 − 8x2 = 27
17x + 10 = 27
17x = 17
x = 1
Vậy x = 1
d) 5x ( 12x + 7 ) − 3x ( 20x − 5 ) = − 100
602 + 35x − 602 + 15x = − 100
50x = − 100
x = −100:50
x = −2
Vậy x = −2
e) 0,6x(x − 0,5) − 0,3x(2x + 1,3) = 0,138
0,6x2 − 0,3x − 0,6x2 − 0,39x = 0,138
−0,69x = 0,138
x = −0,2
Vậy x = −0,2
