题目

如图 （1） 若 a，b，c，d 是实数，我们规定 ，当时，求 x 的值. （2） 如图，在平面直角坐标系内，O为原点，点A在x轴正半轴上，点B的坐标为(4，3).若tan∠BAO＝sin∠BOA，求点A的坐标. 答案：解：由题可得：|x−1，2x，x+1|=(x−1)(x+1)−2⋅x=x2−2x−1，∵|x−1，2x，x+1|=7，∴x2−2x−1=7，(x−4)(x+2)=0解得：x1=4或x2=−2； 解：如图，过点B作BC⊥OA交于C，∵B(4，3)，∴OC=4，BC=3，∴OB=OC2+BC2=42+32=5，∴sin∠BOA=sin∠BOC=BCOB=35，tan∠BAO=tan∠BAC=BCAC=3AC，∵tan∠BAO=sin∠BOA，∴3AC=35，∴AC=5，∴OA=OC+AC=4+5=9，∴A(9，0 Lead has proved to be a useful metal. 【1】 It goes into car batteries and also helps make bright pigments, used to paint walls, metal work and toys.【2】 In the worst cases it causes comas（昏迷）and death. More often its effects are slow but harmful. Research shows that lead is a threat to little babies, who are most likely to take in dust and paint chips that contain lead. Their brains can be easily harmed. 【3】The dangers of lead have long been known. American banned it from paint 40 years ago, and by the late 1990s leaded petrol had been stopped gradually in almost all rich countries. But the effects continue to exist. 【4】 The situation is more alarming in the poor world, where the use of lead-based paints is spreading. As people in Asia and Africa become richer, they start to decorate their homes, but the paint they use, even from pots labeled "lead-free" often contains it.It is neither difficult nor expensive to stop using lead. 【5】 And industrial use is no exception, because the contamination （污染物）spreads and industrial paint inevitably finds its way into the consumer market. Yet only four sub-Saharan African countries have formally placed bans and local factories are often unaware of the harm that lead causes.A. Yet lead is also a poison.B. It turns up everywhere.C. All countries should ban lead in paint.D. Half a million American children are diagnosed with lead poisoning.E. There is no excuse for poor countries to repeat the mistake of rich ones.F. Taking some simple precautions can help protect you and your family from lead exposure.G. But only years after exposure are the results apparent in lower IQ and learning disabilities.