I. TRẮC NGHIỆM:
1/ Tổng số đo ba góc của một tam giác bằng :
A. 180
0
B. 120
0
C. 360
0
2/ Tam giác ABC có
µ µ
0
B C 45= =
, tam giác ABC là tam giác
A. Tam giác vuông B. Tam giác cân C. Tam giác vuông cân
3/ Tam giác nào là tam giác vuông trong các tam giác có độ dài 3 cạnh như sau:
A. 6m, 8m,12m B. 9m, 15m, 12m C. 7m, 7m, 10m
4/
ABC DEF
∆ = ∆
, biết
µ
µ
0 0
E 30 ;D 70= =
. Số đo của góc C bằng:
A. 80
0
B. 30
0
C. 70
0

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Đáp án
I. Trắc nghiệm:
Câu 1 2 3 4
Đáp án A C B A
II. Tự Luận
K

0
AHB AHC 90 (gt)= =

AB = AC (gt)
AH là cạnh chung
Vậy
AHB AHC∆ = ∆
(cạnh huyền – cạnh góc vuông)
b/ Chứng minh
∆
IHK là tam giác cân
Xét
BIH và CKH∆ ∆
, ta có:
·
·
0
BIH CKH 90= =
(gt)
BH = HC (vì
AHB AHC
∆ = ∆
)
µ µ
B C=
(gt)
Vậy
BIH CKH∆ = ∆
(cạnh huyền – góc nhọn)
⇒

= 25 – 9 = 16
⇒
AH =
16 4cm=