Mathematics
Senior High
349（1）で、なぜこの考え方ではダメなのか教えてください！
答えは6/5です！
E
(3) a=8, b=5, C=60°
349 次のような△ABCにおいて,∠Aの二等分線と辺BCとの交点をDとす
るとき, AD の長さを求めよ。
*(1) b=3,c=2,A=120°
250 M&TT
(2) 6=3,c=4,A=60°
A
349 (1) @A
2
B
D
1200
a² = 2² + 3²2 $₁213 cos (209
=4+9+6
=19
a =√₁9
e
19
x4
7³6
AB=AC = BP = CD
2 = 3 = x=(√₁9-x)
32 = 2√/19-2x
x = 2/19
5
(²1²) ²= 2²+ AP²= 2 · B-AD-Cos60°²
76
222 25 = 4 + AD ²-2AD
25
100
24
AD²=2AD + 3² / 1² = 0
25
96 = 100+25AB²-SOAD
2
25 AD ²50AD + 24 = 0
(SAD-6) (SAD-4)=0
64
AD = £², +
5
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