RADON GAS

(7) _____________ most people are aware of the dangers of radiation, not many consider that they might be at
risk in their own homes from radon, a naturally occurring radioactive gas. (8) _____________ it is colorless and
odourless, home owners may not be aware of potential problems. However, radon is (9) _____________ dangerous
that in the USA alone it is the second most common cause of lung cancer. (10) _____________ there are no immediate
symptoms of exposure, which may take years to surface, it's as well to have your house tested if you are in a risk area.

a² + 2ab + b² - 2a - 2b

= (a² + 2ab + b²) - (2a + 2b)

= (a + b)² - 2(a + b)

= (a + b)(a + b - 2)

Khi chuyển một số hạng từ vế này sang vế kia của một bất đẳng thức ta phải đổi dấu số hạng đó, cụ thể: dấu "+" thành dấu "-" và ngược lại.