2021年七年級(jí)下冊(cè)期中數(shù)學(xué)試題參考答案及評(píng)分標(biāo)準(zhǔn)
一、選擇題（本大題共10個(gè)小題，每小題3分，共30分）
二、填空題（本大題共5個(gè)小題，每空3分，共18分）
11. . 12. 如果兩個(gè)角相等，那么它們的余角也相等.
13. 4. 14. 5，75° 15. 52.5°
三、解答題（本大題含8個(gè)小題，共72分）
16.（本題8分）
（1）解：原式 ··· ·········· ············ ···································（2分）
= ····· ·························································（4分）
解：原式 = ··· ·········· ············ ···································（2分）
= ····· ·························································（4分）
y
x
17. （本題8分）
解：
如圖所示 ··· ·········· ············ ···································（2分）
左，4； 上，2； ··· ·········· ············ ···································（6分）
如圖所示 ··· ·········· ············ ···································（8分）
18.（本題6分）
解：依據(jù)1：對(duì)頂角相等 ··· ·········· ············ ···································（1分）
依據(jù)2：同旁內(nèi)角互補(bǔ)，兩直線平行 ······· ············ ···································（2分）
∠C , 依據(jù)3：兩直線平行，同旁內(nèi)角互補(bǔ) ········································（4分）
依據(jù)4：內(nèi)錯(cuò)角相等，兩直線平行 ··········· ············ ···································（5分）
依據(jù)5：兩直線平行，內(nèi)錯(cuò)角相等 ··········· ············ ···································（6分）
19.（本題8分）


如圖所示 ········ ··································（3分）
（3,0）; （0，-1）；（4，-2） ··········································（6分）
··········································（8分）
20.（本題10分）
解： （1）3； ····································································（4分）
（2） 即
∴的整數(shù)部分為4，
小數(shù)部分為（），即a=; ························································（6分）
，即
∴的整數(shù)部分為5，即b=5 ······················································（7分）
∴==1 ······················································（8分）
（3）則的相反數(shù)是 ． ··············································（10分）
21.（本題8分）
解：（1）當(dāng)h＝1.7時(shí)，S2＝1.7×1.7， ··· ·········· ············ ···································（2分）
∴S＝﹣1.7（舍）或S＝1.7， ··· ·········· ············ ···································（3分）
答：當(dāng)眼睛離海平面的高度是1.7m時(shí)，能看到約1.7km遠(yuǎn)； ····························（4分）
（2）當(dāng)S＝1.7×3＝5.1時(shí)，可得5.12＝1.7h， ······ ···································（5分）
解得h＝15.3， ························································（6分）
15.3﹣1.7＝13.6（米）， ························································（7分）
答：觀望臺(tái)離海平面的高度約為13.6米． ························································（8分）
（本題12分）
（1）過點(diǎn)C作CG∥DF
∴∠DFE=∠FCG ························································（1分）
∵BC⊥MN
∴∠BCF=90°
∴∠BCG+∠FCG=90° ························································（2分）
∴∠BCG+∠DFE=90°
∵∠ABC+∠DFE=90°
∴∠ABC=∠BCG ························································（3分）
∴CG∥AB
∴DF∥AB ························································（4分）
（2）解：∵∠ABC=∠ACB，∠DEF=∠DFE，
又∵∠ABC+∠DFE=90°
∴∠ACB+∠DEF=90° ························································（6分）
∵BC⊥MN
∴∠ACE=90°
∴∠ACB+∠ACE=90°
∴∠DEF=∠ACE ························································（7分）
∴DE∥AC ························································（8分）
如圖三角形DEF即為所求
························································（10分）
2α ·······················································（12分）
23.（本題12分）
（1）（﹣8，）； ························································（2分）
平行 ························································（4分）
（2）①t= ························································（6分）
② ························································（10分）
③-4 ························································（12分）
題號(hào)
1
2
3
4
5
6
7
8
9
10
答案
B
C
A
D
D
B
C
B
D
D

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