a)..... cm đc rùi
b) ta có tam giác ABC cân tại A có AH là đường cao=> AH đồng thời là đường trung tuyến
=> HB=HC=18:2=9cm
\(AH^2=AB^2-HB^2=15^2-9^2=225-81=144\)
\(AH=\sqrt{144}=12cm\)
\(BG^2=4^2+9^2=16+81=97\)
rua ak. Giai giup tau bai tao ms dang len kai
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