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提问人:网友l******8 发布时间:2022年5月1日 22:41
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设,证明f(x,y)在(0,0)处一阶偏导数存在但不可微

设 ,证明f(x,y)在(0,0)处一阶偏导数存在但不可微

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Saudi Arabia, the oil industry's swing producer, has become its flip-flopper. In February, it persuaded OPEC to cut its total production quotas by 1m barrels per day (bpd), to 23.5m, as a precaution against an oil-price crash this spring. That fear has since been replaced by its opposite. The price of West Texas crude hit $40 last week, its highest since the eve of the first Iraq war, prompting concerns that higher oil prices could sap the vigour of America's recovery and compound the frailty of Europe's. On Monday May 10th, Ali al-Naimi, Saudi Arabia's energy minister, called on OPEC to raise quotas, by at least 1.5m bpd, at its next meeting on June 3rd. Thus far, the high oil price has been largely a consequence of good things, such as a strengthening world economy, rather than a cause of bad things, such as faster inflation or slower growth. China's burgeoning economy guzzled about 6m bpd in the first quarter of this year, 15% more than a year ago, according to Goldman Sachs. Demand was also strong in the rest of Asia, excluding Japan, growing by 5.2% to 8.1m bpd. As the year progresses, the seasonal rhythms of America's drivers will dictate prices, at least of the lighter, sweeter crudes. Americans take to the roads en masse in the summer, and speculators are driving up the oil price now in anticipation of peak demand in a few months' time. Until recently, the rise in the dollar price of oil was offset outside America and China by the fall in the dollar itself. But the currency has regained some ground in recent weeks, and the oil price has continued to rise. Even so, talk of another oil-price shock is premature. The price of oil, adjusted for inflation, is only half what it was in December 1979, and the United States now uses half as much energy per dollar of output as it did in the early 1970s. But if oil cannot shock the world economy quite as it used to, it can still give it 'a good kick', warns Goldman Sachs. If average oil prices for the year come in 10% higher than it forecast, it reckons CDP growth in the Group of Seven (CT) rich nations will be reduced by 0.3%, or $70 billion. The Americans are certainly taking the issue seriously. John Snow, their treasury secretary, called OPEC's February decision 'regrettable', and the rise in prices since then 'not helpful'. Washington pays close heed to the man at the petrol pump, who has seen the average price of a gallon of unleaded petrol rise by 39 cents in the past year. And the Saudis, some mutter, pay close heed to Washington. Besides, the high oil price may have filled Saudi coffers, but it has also affronted Saudi pride. Mr. al-Naimi thinks the high price is due to fears that supply might be disrupted in the future. These fears, he says, are 'unwarranted'. But the hulking machinery in the Arabian desert that keeps oil flowing round the world presents an inviting target to terrorists should they tire of bombing embassies and nightclubs. On May 1st, gunmen killed six people in a Saudi office of ABB Lummus Global, an American oil contractor. Such incidents add to the risk premium factored into the oil price, a premium that the Saudis take as a vote of no confidence in their kingdom and its ability to guarantee the supply of oil in the face of terrorist threats.What does the author mean by '...has become its flip-flopper'(Para. 1)?A.Saudi Arabia reversed its earlier decision.B.Saudi Arabia objected to the rise of oil price.C.Saudi Arabia was concerned about the world economy.D.Saudi Arabia wished to reduce the oil production.
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