證明：過(guò)點(diǎn)?$O$?作?$OC⊥AB，$?垂足為點(diǎn)?$C$?
∵?$OA=OB，$??$OC⊥AB$?
∴?$ AC=\frac 12AB=12\ \mathrm {cm}$?
?$ $?在?$Rt△AOC$?中，?$ OC=\sqrt {AO^2-AC^2}=5\ \mathrm {cm}$?
∵圓?$O$?的直徑為?$10\ \mathrm {cm}，$??$OC=5\ \mathrm {cm}$?
∴點(diǎn)?$C$?在圓?$O$?上
∴?$AB$?是圓?$O$?的切線
