Tai sao ban nen cho minh cach giai nhe 

1h15'=75p

\(SP=\frac{75\cdot30}{45}=\frac{3.5.5.3.10}{9.5}=50\left(Sp\right)\) luoi chia pt ra luon 

25 dung roi

A) 39,7 x 2,5 + 7,5 x39,7=

=(2,5+7,5) x 39,7

=10 x 39,7 

=397

B)84,69 x 125 - 84,69 x 55 + 30 x 84,69=

=(125 - 55 + 30 ) x 84,69

=100 x 84,69

=8469

Nhớ k cái dấu đúng cho mình <3

l lít = 1dm³

*** mk nha

con người

\(\left(x^2+2x+8\right)=y^2.\)

\(\left(x+1\right)^2-y^2=-7\)

\(\left(x-y+1\right)\left(x+y+1\right)=-7\)

+\(\hept{\begin{cases}x+y+1=7\\x-y+1=-1\end{cases}\Leftrightarrow\hept{\begin{cases}x+y=6\\x-y=-2\end{cases}\Leftrightarrow}\hept{\begin{cases}x=2\\y=4\end{cases}}}\)

+\(\hept{\begin{cases}x+y+1=1\\x-y+1=-7\end{cases}\Rightarrow\hept{\begin{cases}x+y=0\\x-y=-8\end{cases}\Leftrightarrow}\hept{\begin{cases}x=-4\left(L\right)\\\end{cases}}}\)

Vậy x =2