22.如圖,在等腰△ABC中,已知AB=AC=5,BC=6,D為AB上一點(diǎn),過(guò)點(diǎn)D作DE⊥AB交BC邊于點(diǎn)E,過(guò)點(diǎn)E作EF⊥BC交AC邊于點(diǎn)F.
(1)求cosB的值;
(2)當(dāng)BD長(zhǎng)為何值時(shí),以點(diǎn)F為圓心,線(xiàn)段FA為半徑的圓與BC邊相切;
(3)過(guò)點(diǎn)F作FP⊥AC,與線(xiàn)段DE交于點(diǎn)G,設(shè)BD長(zhǎng)為t,△EFG的面積為S,求S關(guān)于t的函數(shù)表達(dá)式及t的取值范圍.