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数学 高校生

定数kは何を表しているのですか?

000 とな 辺を引 りを 解決 数) 有点 式 (2) で 2. 曲線の交点を通る曲線の方程式(1) 一般に、次のことが成り立つ [曲線/(x, y)()については、166の解説も参照」。 異なる曲線/(x,y)=0g(x,y)=0がいくつかの交点をもつとき 方程式kf(x,y)+g(x,y)=0 (kは定数) ・・・・・・ (A)は,それらの交 すべてを通る曲線を表す [ただし、曲線(x,y)=0を除く]。 例題 106 (2) で方程式 k+g=0 を利用する理由 169 (1)で2円の共有点の座標が求められたので, か.150 例題 94 のように、円の方程式の 一般形x+y+lx+my+n=0に通る3点 (1,2), (-2,-1), (1,0)の座標を代入 は計算が面倒になることもある。 後はんの1次方程式を解けばよいから,計算も簡単に進められて都合がよい。 足 1.ここで, 上の (*) が成り立つ理由について考えてみよう。 2曲線はともに点Aを通るから,f(xi, yi)=0,g(x,y)=0が 2曲線がn個の交点A(x, y) (i= 1, 2,......, n) をもつとする。 ともに成り立つ。よって, kの値に関係なく, kf(Xi, Vi)+g(x,y)=0が成り立つ。 すなわち、Aの表す曲線は点A(i=1, 2,......, n) を通る。 しかし、曲線f (x, y) =0上で交点以外の点をP(s, t) とすると, f(x, y) は f(x, y) に x=x y=ys を代入したと きの値。 f(s,t)=0かつg(s,t) ≠0 であるから, kf(s,t)+g(s,t) =0を満たすんは存在しない。 すなわち, 方程式 Aが曲線f (x, y) =0を表すことはない。 補足2. 方程式kf+g=0 を利用する際は、次のことも意識するようにしておきたい 2曲線f (x,y)=0,g(x, y) = 0 が共有点をもつかどうか。 2曲線の方程式のうち,形の簡単な方を f(x, y) = 0 とする。 座標を代入した後の計算をらくにするための工夫。 前提条件を忘れずに ここで2曲線f(x,y)=0,g(x,y)=0が, [1] ともに直線 [2] ともに円 の場合を考えると,それぞれ次のようになる。 [1] 交わる2直線αx+by+c=0,ax+by+c2=0 に対し, 方程式 kax+by+c+ax+by+c2=0 は、2直線の交点を通る直線を表す(直線ax+by+c=0を除く)。 [2] 異なる2点で交わる2円 x 2 +y+hx+miy+m=0, x2+y2+bx+mzy+n2=0に対し, 方程式 kx+y+hx+my++x+y+lx+my+n=0 Bは、 k=1のとき2つの交点を通る直線 (2円の共通弦を含む直線) kキー1のとき2つの交点を通る円(円x2+y'+hx+miy+m=0を除 を表す。

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英語 中学生

英語の長文についてです。 写真↓の長文の音読に10分も時間がかかりました。5分に縮めるための解決策を教えて下さい。 ○今の自分の読み方 ・読んでいるところを見失わないように指でなぞる ・英文を1語1語読み込みすぎない ・英文を和訳するときに戻り読みをしてない        ... 続きを読む

都立プレOP 1015 次の文章を読んで, あとの各問に答えなさい。 3 (*印がついている単語・語句には、本文のあとに 〔注〕 がある。) Food is useful and delicious. It gives us energy for daily life and many good things for our bodies. But if we do not take care of food, we may get *food poisoning. So, how can food *stay good for a longer time? And what can you do at home to make your food safe? Fresh food does not stay good for a long time. Many foods *go bad in a few days. Some change fast even in a few hours. Warm weather and water make this problem bigger. Very small living things can grow on food and in food. These living things are *microorganisms, and some of them are *bacteria. They can come from the air, hands, tools, and tables. When they become many, food can change. The color can change, and a strange *smell may appear. So people keep creating many ways to *preserve food. This means that food stays good longer, and it is safer to eat. One of the oldest ways is drying. Drying takes water out of food. With less water, microorganisms do not grow fast. Then food can stay good longer. Look at Picture 1. Long ago, people put food under the sun and in the wind for many hours. Dried fish and dried fruit are good examples. Drying makes food light and (1)-a So dried food was useful for travelers on long trips. However, dried food can change quickly after it becomes wet again. So people needed a dry place and a closed bag. 1 II Li Drying can also change the *taste and the feeling in the mouth. For example, grapes can become (1)-b Dried grapes taste good. On the other hand, when a bag of dried food is open on a very easy to carry very small and sawetan take in water. Then it may not taste good, and bacteria may start to grow. After that, the food may go bad soon. boll To make food drier, people used more ideas than just the sun and wind. One idea was salt. Salt could pull water out of food, and the food could become drier. For example, people put salt on fish, and then they put it outside. The fish became dry and very salty. It stayed good for many days, so people could eat it later. Before cooking, people often washed the fish in water, and some salt went away. Another idea was *smoke from a fire. People hung meat or fish over a small fire for many hours. The smoke made the food drier, and it could give a special smell and taste. This food stayed good longer than fresh food. But if the inside was still wet, it could go bad. These ways are still used today in many places.00 yw yron al sobi blo Another old idea is cooling. When the temperature goes down, changes in food become slower. Bacteria also grow more slowly. Today, many homes have a *fridge, but long ago, people used nature. In cold areas, people used snow and ice. In other places, people used cool places in the mountains or cold river water. Later, people built special places for ice. They put ice in ice houses with thick walls, and the ice stayed (1)-c . Look at Picture 2. In Japan, people built a special building. It was a himuro. They used it old for many mice for the summer. In winter, they brought snow and ice from cold places and put them inside. Even today, the same idea is useful. An *ice pack can alad be(2) But it slowly turns cool a lunchbox for some time. 9

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