[toán 9] tìm AB

N

nguyenbahiep1

[laTEX]cosB = \frac{1}{2} = \frac{AB^2+BC^2-AC^2}{2AB.BC} \\ \\ \begin{cases}AB^2-AC^2 + 64 = 8.AB \\ AB+AC= 12 \end{cases} \\ \\ AB = 5 , AC = 7 [/laTEX]
 
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