de bai co noi tinh = cách nào ko .

a) 2 x 53 x 12 + 4 x 6 x 83 - 3 x 8 + 40

= (2 x 12) x 53 + ( 4 x 6 ) x 83 - ( 3 x 8 ) + 40

= 24 x 53 + 24 x 83 - 24 + 40

= 1272 + 1992 - 64

= 3264 - 64 = 3200

=

a) (3x + 2)(x^2 - 1) = (9x^2 - 4)(x + 1)

<=> 3x^3 - 3x + 2x^2 - 2 = 9x^3 + 9x^2 - 4x - 4

<=> 3x^3 - 3x + 2x^2 - 2 - 9x^3 - 9x^2 + 4x + 4 = 0

<=> 6x^3 + 7x^2 - x - 2 = 0 (doi dau)

<=> (x + 1)(2x - 1)(3x + 2) = 0

<=> x + 1 = 0 hoặc 2x - 1 = 0 hoặc 3x + 2 = 0

<=> x = -1 hoặc x = 1/2 hoặc x = -2/3

16:Sửa đề: \(\frac12x+\frac16\left(x-2\right)=\frac34-2x\)

=>\(\frac12x+\frac16x-\frac26=\frac34-2x\)

=>\(\frac46x-\frac13=\frac34-2x\)

=>\(\frac23x+2x=\frac34+\frac13\)

=>\(\frac83x=\frac{9}{12}+\frac{4}{12}=\frac{13}{12}\)

=>\(x=\frac{13}{12}:\frac83=\frac{13}{12}\times\frac38=\frac{13}{4\times8}=\frac{13}{32}\)

19: \(\frac{5}{12}x+3=\frac13-\frac{7}{12}x\)

=>\(\frac{5}{12}x+\frac{7}{12}x=\frac13-3\)

=>\(\frac{12}{12}x=\frac13-\frac93=-\frac83\)

=>\(x=-\frac83\)

20: \(\frac12x+\frac52=\frac72x-\frac34\)

=>\(\frac12x-\frac72x=-\frac34-\frac52\)

=>\(-3x=-\frac34-\frac{10}{4}=-\frac{13}{4}\)

=>\(3x=\frac{13}{4}\)

=>\(x=\frac{13}{4}:3=\frac{13}{12}\)

bay bài đó với

x/2 = y/3 = z/-4

Đặt: x/2 = y/3 = z/-4 = k

x = 2k; y = 3k; z = -4k

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