\(24\cdot76+48\cdot12-20\cdot100=24\cdot76+24\cdot2\cdot12-20\cdot100\)

                                                     \(=24\cdot\left(76+2+12\right)-20\cdot100\)

                                                     \(=24\cdot100-20\cdot100\)

                                                     \(=\left(24-20\right)\cdot100\)

                                                     \(=4\cdot100=400\)

Cảm ơn bạn nhiều nha

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\(\dfrac{x-90}{10}+\dfrac{x-76}{12}+\dfrac{x-58}{14}+\dfrac{x-36}{16}+\dfrac{x-15}{17}=15\)

\(\Leftrightarrow\dfrac{x-90}{10}-1+\dfrac{x-76}{12}-2+\dfrac{x-58}{14}-3+\dfrac{x-36}{16}-4+\dfrac{x-15}{17}-5=0\)

\(\Leftrightarrow\dfrac{x-100}{10}+\dfrac{x-100}{12}+\dfrac{x-100}{14}+\dfrac{x-100}{16}+\dfrac{x-100}{17}=0\)

\(\Leftrightarrow\left(x-100\right)\left(\dfrac{1}{10}+\dfrac{1}{12}+\dfrac{1}{14}+\dfrac{1}{16}+\dfrac{1}{17}\right)=0\)

\(\Leftrightarrow x-100=0\) (do \(\dfrac{1}{10}+\dfrac{1}{12}+\dfrac{1}{14}+\dfrac{1}{16}+\dfrac{1}{17}\ne0\))

\(\Leftrightarrow x=100\)

\(\frac{X-90}{10}+\frac{X-76}{12}+\frac{X-58}{14}+\frac{X-36}{16}+\frac{X-15}{17}=15\)

\(\frac{X-90}{10}+\frac{X-76}{12}+\frac{X-58}{14}+\frac{X-36}{16}+\frac{X-15}{17}-15=0\)

\(\frac{X-90}{10}-1+\frac{X-76}{12}-2+\frac{X-58}{14}-3+\frac{X-36}{16}-4+\frac{X-15}{17}-5=0\)

\(\frac{X-100}{10}+\frac{X-100}{12}+\frac{X-100}{14}+\frac{X-100}{16}+\frac{X-100}{17}=0\)

\(\left(X-100\right).\left(\frac{1}{10}+\frac{1}{12}+\frac{1}{14}+\frac{1}{16}+\frac{1}{17}\right)=0\)

=> X-100=0

=> X=100

vậy x=100

1a) -54 . 76 + 12 .(-76) + 76.(-34)

= (-54 - 12 - 34).76

= -100 . 76

= -176

b) 37.(63 - 24) - 63.(24 + 37)

= 37 . 63 - 37 . 24 - 63.24 - 63 . 37

= (37.63 - 63.37) - (37 + 63) . 24

= 0 - 100 . 24

= - 2400

2a) x + (-27) = -23 - x

=> x + x = -23 + 27

=> 2x = 4

=> x = 4 : 2

=> x = 2

b) xy + 2x - y = 15

=> x(y + 2) - y = 15

=> x(y + 2) - (y + 2) = 13

=> (x - 1)(y + 2) = 13 = 1 . 13 = 13 . 1

Lập bảng :

Vậy ...

\(=20,15\times\left(23+76+1\right)=20,15\times100=2015\)

=20,15x(23+76+1)

=20,15x100

=2015

Đây nha