Đáp án:
Áp dụng bất đẳng thức tam giác:
Ta có: `AB - BC < AC < AB + BC`
hay `12 - 6 < AC < 12 + 6`
`⇒ 6 < AC < 18`
Vì ΔABC là tam giác cân nên `AC = AB = 12 cm` hoặc `AC = BC = 6cm`
Mà `6 < AC < 18`
`⇒ AC = 12 cm`
Vậy `AC = 12cm`
Học tốt
$#DUCK$Xét Δ cân $ABC$ có:
$AB$ $=$ $AC$( Tính chất Δ cân)
Mà $AC$ $=$ $12$ $cm$
$→$ $AB$ $=$ $12$ $cm$
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