Maths ！！急救急救！！

15.
angle BCF=83(alt angles,EG//BD)
angle CAB=61(ext angle of tri.)
a=119(adj angles on a st line)
18.
to jot a st line CF//DE//AB
angle Fcd=50(int angles,CF//DE)
c+50=120(alt angles,CF//AB)
c=70
19.because angleA=angleC
so 5x=3x+4(2sides opp equal angle)
2x=4
x=2
perimeter
=5x+3x+3x+4
=11x+4
=26 cm

2011-03-05 18:36:07 補充：
typing error:
because angle A=angle C
so 5x=3x+4(base angle,isos.tri.)

15)angle DCM=angle GFC =83度(corr.angles,EG//BD)
83度+angle BCM=180度(adj.angles on st.line)
angle BCM=97度

a=angle CBA+angle BCM=22度+97度=119度

18)Draw a line FG s.t.(such that)parallel to AB & DE.
120度+angle FCB=180度(int.angles,FG//AB)
angle FCB=60度
130度+angle GCD=180度(int.angles,FG//DE)
angle GCD=50度
60度+50度+c=180度(adj.angles on st.line)
c=70度

19)(a)(數學符號"因為")angle A=angle C
(數學符號"所以")AB=BC
5x=3x+4
x=2

(b)perimeter of triangle ABC
=5(2)+[3(2)+4]+3(2)
=26cm.

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