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Every ten minutes, one kind of animal, plant or insect dies out. for ever. If nothing is done about it, one million species that are alive today will have become extinct twenty years from now.
The seas are in danger They are being filled with poison: industrial and nuclear waste., chemical fertilisers and pesides, sewage. The Mediterranean is already nearly dead; the North Sea is following. If nothing done about it, one day soon nothing will be able to live in the seas.
The tropical rain forests, which are the origin of half the earth’s living things( including many rare animals and plants), are being destroyed. If nothing is done about it, they will have nearly disappeared in twenty years. The effect on the world’s climate – and on our agriculture and food supplies – will be disastrous.
Fortunately, somebody is trying to do something about it. In 1961, the World Wildlife Fund was founded - a small group of people who wanted to raise money to save animals and plants from extinction. Today, the World Wildlife Fund is a large international organisation. It has raised over 35 million pounds for conservation projects, and has created or given support five continents. It has helped 30 mammals and birds – including the tiger – to survive Perhaps this is not much, but it is a start. If more people give more money – and if more governments wake up to what is happening – perhaps the World Wildlife Fund will be able to help us to avoid the disaster that threatens the natural world, and all of us with it.
Diện tích 1 viên gạch là :
25 × 20 = 500 cm²
Diện tích cả căn phòng là :
2 ×4 ×( 10,6 +5,8 ) = 131,2 m² = 131200 cm²
Diện tích của cửa ra vào là :
1,2 × 2,25 = 2,7 m² = 2700 cm²
Diện tích 2 của sổ là :
2 × 1,8 × 1,25 = 4,5 m² = 4500 cm²
Diện tích tường là :
131200 - 4500 - 2700 = 124000 cm²
Số viên gạch cần là :
124000 ÷ 500 = 248 viên
Đáp số : 248 viên
\(|x-1|=|x+2|\)
Nếu x>=1; ta có:
x-1= x+2 -> vô nghiệm
Nếu x<1 và x>=-2. ta có:
-x+1=x+2-> x=-1/2
Nếu x<-2; ta có
-x+1= -x-2 -> Vô nghiệm.
Vậy đáp số x=-1/2
| x - 1 | = | x + 2 |
Với x < -2 pt <=> -( x - 1 ) = -( x + 2 ) <=> -x + 1 = -x - 2 ( vô nghiệm :)) )
Với -2 ≤ x < 1 pt <=> -( x - 1 ) = x + 2 <=> -x + 1 = x + 2 <=> -2x = 1 <=> x = -1/2 ( tm )
Với x ≥ 1 pt <=> x - 1 = x + 2 ( vô nghiệm :)) )
Vậy phương trình có nghiệm duy nhất x = -1/2
\(A=\frac{9}{\frac{n}{5}}=9\div\frac{n}{5}=\frac{45}{n}\)
Ta có : \(Ư\left(45\right)=\left\{\pm1;\pm3;\pm5;\pm9;\pm15;\pm45\right\}\)
Số số nguyên n để A là số nguyên là : 6 * 2 = 12 ( số )
Đ/s : 12 số