a) Xét hai tam giác vuông ABH và CAH có:\widehat{ABH} = \widehat{HAC} ( cùng phụ \widehat{BAH}\rightarrow \Delta ABH \sim \Delta CAH\rightarrow \frac{AH}{CH} = \frac{BH}{AH}\rightarrow AH2 = HB.HCABH^=HAC^" role="presentation" style="display: inline-block; line-height: normal; font-size: 18px; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; color: rgb(51, 51, 51); font-family: 'times new roman'; position: relative;">ABH^=HA (cùng phụ với góc BAHBAH^" role="presentation" style="display: inline-block; line-height: normal; font-size: 18px; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; color: rgb(51, 51, 51); font-family: 'times new roman'; position: relative;">BAH^Do đó, ΔABH∼ΔCAH" role="presentation" style="display: inline-block; line-height: normal; font-size: 18px; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; color: rgb(51, 51, 51); font-family: 'times new roman'; position: relative;">ΔABH∼ΔCAH⇒AH2=BH.CH" role="presentation" style="display: inline-block; line-height: normal; font-size: 18px; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; color: rgb(51, 51, 51); font-family: 'times new roman'; position: relative;">
a) Xét hai tam giác vuông ABH và CAH có:
$\widehat{ABH}
$ =
$\widehat{HAC}
$ ( cùng phụ
$\widehat{BAH}
$$\rightarrow \Delta ABH \sim \Delta CAH
$$\rightarrow \frac{AH}{CH}
$ =
$\frac{BH}{AH}
$$\rightarrow
$ AH2 = HB.HCABH
^=HAC
^" role="presentation" style="display: inline-block; line-height: normal; font-size: 18px; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; color: rgb(51, 51, 51); font-family: 'times new roman'; position: relative;"
>ABH^=HA (cùng phụ với góc BAHBAH
^" role="presentation" style="display: inline-block; line-height: normal; font-size: 18px; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; color: rgb(51, 51, 51); font-family: 'times new roman'; position: relative;"
>BAH^Do đó,
ΔABH
∼ΔCAH" role="presentation" style="display: inline-block; line-height: normal; font-size: 18px; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; color: rgb(51, 51, 51); font-family: 'times new roman'; position: relative;"
>ΔABH∼ΔCAH
⇒AH2=BH.CH" role="presentation" style="display: inline-block; line-height: normal; font-size: 18px; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; color: rgb(51, 51, 51); font-family: 'times new roman'; position: relative;"
>