. Tinh cdc cqnh ctia khiii ch6p S.ABN. Ta c6
t
AN = BN = I AC = aJL, sB =,[s,(id = 4o,Z Z
sN =.,EF|M =allp,-v6,y a(la,sw)
_ !2V,.ABN _?nJg
-r - 13
ll\
Thi d1l 5. (Tqp chi TH&TT tii 455, thang 5 ndm 2015, trang 7). Cho hinh chop S.ABCD c6 day ABCD la hinh chir nhdt vcti AB: a,BC = ali .
Hai mQt phdng (SAQ vd (SBD) ci.mg wdng g6c voi day. Di6m I thu6c doan SC sao cho SC:3C1. Tinh th€ tich khrii chdp S.ABCD vd khodng
cach giira hai dadng thdng AI vd SB bi& rdng
AI vudng goc vni SC. ^t C'
D'
Hinh 4
Ldi gidi. (h.a)
. Tinh thA tich cfia t* di€n AMND .
Ta c6 d (N,(AlrID)) = o, S n,o =)nr.* = |Ia2a' Ia2a'
) Vn^o =Vtu.ot.ro = j.o.? =;r,.
' Tinh c5c c4nh cria tu diQn AMND. Ta c6AM =1, ur=a, DM =+,lN=DN=*, AM =1, ur=a, DM =+,lN=DN=*, MN=$ vav a(,tN,ou) J2\ _ lzv*,up _2nJS . - -15 Thi d1t A. Qrlch Ei thi Dqi hqc kh\i A ndm
2011). Cho hinh chop
SABC c6 day (ABC) ld
tam gidc vu6ng cdn tgi B,
AB : BC :2a; hai rndt
phdng $AB) vd (SAQ cirng vu6ng g6c vdi mql
phdns \aq. Gqi M td trung di€m cfia AB, mQt
aJ3
Hinh 6
Hmfmg ddn. $.6)' Ggi O ld tdm cua hinh chfi
nh\tABCD. Tri gi6 thiiit c6 SO L(ABCD). Tir AC:"[AE +Be :2a >N=a; SC:3IC;
AI L SC = LS}C C, MIC (g.g) = # = #o'JB o'JB J dJE B Hinh 5
phdltg qua SMvd song song vai BC, cdt AC tqi.N. Bi€t gdc girta hai mfit phdng (SBQ vd (ABQ bdng
60'. Tinh khodng cach giira hai dadng thdng AB vd SN theo a.
Ldi gi,rti (1r.5). Tt gri thi6t c6: SAI(ABC).
AB LBC=SB LBC>GA hg6c gita(SBg vd
+,SC =aJ6 =^tO =oJS )Vs.,qBco=
. T{nh thd fich khdt chop S.ABI.Vr.^ Vr.^