Câu `1`
`a,` Đề sai
`b,2/5` $\times $ `5/9 + 4/9` $\times $ `2/5 - 2/5`
`= 2/5` $\times $ `(5/9+4/9-1)`
`= 2/5` $\times $ `0`
`= 0`
`c,S = (1-1/2)` $\times $ `(1 - 1/3)` $\times $ `(1-1/4)` $\times $ ... $\times $ `(1-1/2024)` $\times $ `(1 - 1/2025)`
`= 1/2` $\times $ `2/3` $\times $ `3/4` $\times $ ... $\times $ `2023/2024` $\times $ `2024/2025`
`= 1/2025`

Câu `2`
`a, x + 4/7 = 9/5`
`x = 9/5 - 4/7`
`x = 63/35 - 20/35`
`x = 43/35`
`b, 35 + 2` $\times $ `(x+2) = 9 : 0,2`
`35 + 2` $\times $ `(x+2) =45`
`2` $\times $ `(x+2) = 45-35`
`2` $\times $ `(x+2)=10`
`x+2=10:2`
`x+2=5`
`x=5-2`
`x=3`

\(4x^2-y^2+4y-4\)

\(=\left(2x\right)^2-\left(y^2-4y+4\right)\)

\(=\left(2x\right)^2-\left(y-2\right)^2\)

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

\(2x^5-50x^3=0\)

=>\(2x^3\left(x^2-25\right)=0\)

=>\(x^3\left(x-5\right)\left(x+5\right)=0\)

=>\(\left[{}\begin{matrix}x^3=0\\x-5=0\\x+5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=5\\x=-5\end{matrix}\right.\)

Bổ sung kết luận:

Vậy \(x\) \(\in\) {-5; 0; 5}

\(x^5-2x^4+x^3\)

\(=x^3\cdot x^2-x^3\cdot2x+x^3\cdot1\)

\(=x^3\left(x^2-2x+1\right)=x^3\left(x-1\right)^2\)

   (\(x^2\) -  4\(xy\) + 4y²) - 25

= (\(x\) - 2y)² - 25

= (\(x-2y\) - 5)(\(x-2y\) + 5)

\(\left(2,6:0,2+1,5\times2\right):2-7\dfrac{1}{2}:\dfrac{3}{2}\)

\(=\dfrac{\left(13+3\right)}{2}-\dfrac{15}{2}\times\dfrac{2}{3}\)

\(=\dfrac{16}{2}-\dfrac{15}{3}=8-5=3\)

a)(2,6:0,2+1,5x2):2-7
=(13+3):2-7
=16:2-7
=8-7
=1
b)1/2:3/2
=1/2x2/3
=1/3

Sửa đề: 12x37x4+8x41x6+3x22x16

=\(48\cdot37+48\cdot41+48\cdot22\)

\(=48\left(37+41+22\right)=48\cdot100=4800\)

   12 x 37 x 4 + 8 x 41 x 6 + 3 x 22 x 16

= (12 x 4) x 37 + (8 x 6) x 41 + (3 x 16) x 22

= 48 x 37 + 48 x 41 + 48 x 22

= 48 x (37 + 41 + 22)

= 48 x (78 + 22)

= 48 x 100

= 4800

4356 CHỮ P

\(x+\dfrac{2}{4}=\dfrac{3}{6}\\ x+\dfrac{1}{2}=\dfrac{1}{2}\\ x=\dfrac{1}{2}-\dfrac{1}{2}\\ x=0\)

\(x+\)\(2/4\)\(=\)\(\dfrac{3}{6}\)

\(_x\)\(\)         \(=\)\(3/6\)\(-\)\(\dfrac{2}{4}\)

x          =0

\(x\cdot9,63-5,63\cdot x=15,6\)

=>\(x\left(9,63-5,63\right)=15,6\)

=>4x=15,6

=>x=15,6:4=3,9

1.2×x_4.68:1.3:1.2=0.6