( 5Đ)A) SABF = 13,43529949 CM2. 2,5ĐB) ĐẶT SABF = 4SBDF = 4X; SAC...

Bài 9( 5đ)

a) S

ABF

= 13,43529949 cm

²

. 2,5đb) Đặt S

ABF

= 4S

BDF

= 4x; S

ACF

= 5S

CEF

= 5y

A

45S

ABC

; S

ABF

+S

AEF

= 4x + 4y =34S

ABC

S

ADF

+S

ACF

= 3x + 5y =

D

E

20x + 20y = 4S

F

C



ABC

B

12x + 20y = 3S Ta có hệ:

ABC

 S

ABC

= 8x  S

ABC

= 2S

ABF

= 26,87059898 cm

²

. 2,5đ