IV. TlfiN TRINH DAY HOC A OAT VAN OE
2. Phep chia hai sd phurc
• GV neu dinh nghia :
Chia sd phicc c + di cho sdphicc a + bi khdc 0 Id tim sd phicc z sao cho c + di = (a + bi)z. Sdphicc z dugc ggi la thuang trong phep chia c + di cho a + bi vd ki hieu la
• GV dua ra cac cau hdi sau: H6. Tim z sao cho i = 2z H7. Tim z sao cho i = (3i +3)z.
H8. Ta da biet z.z = IzP = a^ + b^. Hay tim - va = .
' ' z z • Thitc hien vi du 1 trong 5' GV sit dung hinh 55 trong SGK
Hoat dgng ciia G V Cau hdi I
Ta cd z = , nghia la gi? 1 + i
Cau hdi 2
Hay tim so phurc lidn hgp ciia 1 + i .
C a u hdi 3
Nhan ca hai ve ciia (*) vdi 1 - i .
H o a t d g n g ciia H S
Ggi y tra Idi cau hdi 1
4 + 2i ^, ., ^ ^. , . , z = o (1 + i)z = 4 + 2i. (*)
1 + i
Ggi y tra Idi cau hdi 2
1 - i
Ggi y tra Idi cau hdi 3
Ta dugc 2z = 6 - 2i. z = 3 - i.
• GV neu cac budc tim thuong cua hai so phiic : De tim thuong z = ta thuc hien cac budc sau:
a + bi
Budc 1. Dua vl dang (a + bi)z = c + di.
Budc 2. Nhan ca hai ve vdi so phiic lien hgp ciia a +bi. Budc 3. z = — jUac +bd) + iad - bc)i]
a +b
• GV neu chii y :
Trong thuc hdnh, detinh thuang —, ta nhdn cd ?«" va mdu vdi sd a + bi
H9. Cho sd phiic z = a + bi. Tim z' ma z'.z = 1.
• Cho sd phiic z = a + bi, sd phiic nghich dao ciia z la z'
a ^ + b ^ a ^ + b ^ • GV neu : Hai sd z va z' ggi la hai sd phirc nghich dao ciia nhau.
HIO. Chiing minh rdng : dl chia z cho z' ta nhan z vdi nghich dao ciia z' • Thuc hien vi du 2 trong 5'.
Hoat dgng ciia GV Cau hdi 1
Tim so phiic nghich dao z ciia 2 + 3i.
Cau hdi 2
Thuc hien phep chia tren.
Hoat dgng ciia HS Ggi y tra Idi cau hdi 1
Ta cd z. (2 + 3i) = 1 « z.l3 = 2-3i 2 3 .
z = 1 .
13 13
Ggi y tra Idi cau hdi 2
HS tu thuc hien bdng each nhan 3 + 2i vdi z.
' Thuc hien "^C 2 trong 5
Hoat dgng ciia GV Hoat dgng cua HS Cau hdi 1 Tfnh 1 + i 2 - 3 i Cau hdi 2 Tfnh 6 + 3i 5i
Ggi y tra Idi cau hdi 1
1 + i _ ( l + i)(2 + 3 i ) _ - l 5_.
2 - 3 i ~ 2^+i-'if " 1 3 " ^ 13^
Ggi y tra Idi cau hdi 2
6 + 3i (6 + 3i).(-5i) 15 30. 5i 25 25 25
• GV cd the tong kit .c + di 1 a + bi a^+b^Ll^d -b^ c ) (^ +\ u dj b^ 1
HOAT DONG 3