关于原点对称的点的坐标PPT课件

kill the witch himself.
5. While _s_i_tt_i_n_g_ by a pool, Ferdinand sees a frog. While he is sitting by a pool, Ferdinand sees a frog.
Grammar2–2.Exercises
A. having added
B. to add
C. adding
D. added
C: The visiting Minister expressed his
satisfaction with the talks and added that
he had enjoyed his stay here.
Grammar2 –1.Filling in the blanks
Complete the sentences with the correct form of the verbs below and rewrite them.
think know sit see leave
1. On_s_e_e_in_g_ her, the king immediately falls in love with her. When the king sees her, he immediately falls in love with her
图 14
1．若点 A(2x－5,6)与点 B(3,2y－7)关于原点对称，则 x＝
1 ____1____，y＝_____2___.
解析：由题意得22xy－－57＝＝－－36
x＝1 ，解得y＝12
.
2．已知△ABC 各顶点坐标为 A(1,1)，B(－2,0)，C(0,5)，作
出与△ABC 关于原点 O 对称的图形． 解：∵点 A、B、C 的坐标为 A(1,1)，B(－2,0)，C(0,5)，
= Though the old man was poor, he was happy.
用法5： 表示结果，常置于句末 e.g. The boy fell off his bike, breaking his right arm.
用法6： 表示方式或伴随,多置于句末，也可置于句首 e.g. 1) He sat at the table, reading a magazine.
∴点 A、B、C 关于原点的对称点 A′、B′、C′的坐标为
A′(－1，－1)，B′(2,0)，C′(0，－5)．在直角坐标系中描出
点 A′、B′、C′，依次连接即可得△ A′B′C′，图略．
3．如图 2，方格纸中的每个小方格都是边长为 1 个单位的 正方形，在建立平面直角坐标系后，△ABC 的顶点均在格点上， 点 C 的坐标为(4，－1)．
2. He marries her, not _k_n_o_w__in_gwho she really is.
He marries her, but he doesn’t know who she really is.
3. Before _le_a_v_i_n_g_ his kingdom, he calls his son to him.
Choosing:
1.Finding her car stolen, ____D____. A. a policeman was asked to help B. the area was searched thoroughly C. it was looked for everywhere D. she hurried to a policeman for help
D: When she found her car stolen, she hurried to a policeman for help.
2. The visiting Minister expressed his satisfaction with the talks, ____C___
that he had enjoyed his stay here.
2) Laughing and talking, they went into the room.
用法7： 为强调与谓语动词的动作同时发生,在-ing形式 短语前可用连词when, while等;为强调在谓语动 词的动作之前或之后发生,在-ing形式短语前可 用连词before或after
e.g. 1) Be careful when crossing the road.
第 3 课时 关于原点对称的点的坐标
关于原点对称的点的坐标 两个点关于原点对称时，它们的坐标符号相反，即点 P(x， y)关于原点的对称点为 P′__(_－__x_，__－__y.) 注意：关于原点对称是中心对称的特殊情况．
关于原点对称的图形(重点) 例题：已知△ABC 中，A(－2,3)，B(－4,2)，C(－1,1)，在图 1 的坐标中，作出△ABC 及其关于原点对称的△ A′B′C′.
2) Don’t laugh while eating.
3) Before going abroad, he lived here.
4) After watching TV, he went to bed.
用法8： 在-ing形式短语前可用介词on,表示“一…… 就……” e.g. On arriving in Beijing, he went to see his uncle.(= As soon as he arrived in Beijing, he went to see his uncle.) 用法9： 为了强调结果，可在-ing形式前加副词thus e.g. The bus was held up by the snowstorm, thus causing the delay.(= The bus was held up by the snowstorm, and as a result it caused the delay.)
immediatelyห้องสมุดไป่ตู้after another
1.Putting down his shopping bag , Will held out his hand. 2.Will, still watching, saw the cat behave curiously. 3. He crossed the road, keeping his eyes on the spot where the cat had been investigating. 4.Pushing his shopping bag through, he scrambled through himself.
.
1) Choosing 2) Filling 3) Corrections
注意：
动词-ing 形式作状语时，其逻辑主语必 须与句子的主语一致，且必须与句子的 主语是逻辑上的主谓关系，动词-ing 形 式表示的动作是次要动作。（一个主语 多个动作。）
1)Choosing:
Choose the best answer from A, B, C and D, and then rewrite the sentences.
用法10： 在-ing形式短语前可用
though/although表示让步 e.g. Though working very hard, he
couldn’t make enough money to pay off his debt. = Though he worked very hard, he couldn’t make enough money to pay off his debt.
(1)把△ABC 向上平移 5 个单位后得到对应的△A1B1C1，作 出△ A1B1C1；
(2)以原点 O 为对称中心，再作出与△A1B1C1 关于原点 O 对 称的△A2B2C2.
图2
解：(1)△A1B1C1 如图 15，作法略． (2)△A2B2C2 如图 15，作法略．
图 15
4．点 P 关于 y 轴的对称点的坐标是(－1,3)，则点 P 关于原 点的对称点 P1 的坐标是__(_－__1_，__－__3_) _．
3) The boy, being very polite, was loved by many teachers.
用法3： 表示条件，多置于句首 e.g. Working hard, you will succeed.
用法4： 表示让步，多置于句首 e.g. Being poor, the old man was happy.
Before the king leaves, he calls his son to him. 4. After_t_h_in__k_in_g_ about the situation, he decides to kilAl tfhteerwhietcthhihnikms saeblof.ut the situation, he decides to
Grammar1–1. Choosing
Read the following sentences and make a choice.
__2___3_ describe two things happening at the
same time
_1____4_ describe one thing happening
思路导引：先求出△ABC 各顶点 关于原点对称点的坐标，再顺次连接 即可．
图1
自主解答：如图 14. 在坐标系中分别描出 A、B、C 点，并连接 AB、BC、AC. 设点 A 关于原点对称的点为 A′，则 A′(2，－3)． 同理 B′(4，－2)，C′(1，－1)． 再描点，连接 A′B′，B′C′，A′C′，则△ A′B′C′ 为所求作三角形．