24.在△ABC中,D是BC邊上的點(diǎn)(不與點(diǎn)B、C重合),連接AD.
(1)如圖1,當(dāng)點(diǎn)D是BC邊的中點(diǎn)時(shí),S
△ABD:S
△ACD=
;
(2)如圖2,當(dāng)AD平分∠BAC時(shí),若AB=m,AC=n,求S
△ABD:S
△ACD的值(用含m、n的式子表示);
(3)如圖3,AD平分∠BAC,延長(zhǎng)AD到E.使得AD=DE,連接BE,若AC=3,AB=5,S
△BDE=10,求S
△ABC的值.