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a)
\(19^2=\left(20-1\right)^2=20^2-2.20.1+1^2=400-40+1=361\)
\(28^2=\left(30-2\right)^2=30^2-2.30.2+2^2=900-120+4=784\)
\(81^2=\left(80+1\right)^2=80^2+2.80.1+1^2=6400+160+1=6561\)
\(91^2=\left(90+1\right)^2=90^2+2.90.1+1^2=8100+180+1=8281\)
b)
\(19.21=\left(20-1\right)\left(20+1\right)=20^2-1^2=400-1=399\)
\(29.31=\left(30-1\right)\left(30+1\right)=30^2-1^2=900-1=899\)
\(39.41=\left(40-1\right)\left(40+1\right)=40^2-1^2=1600-1=1599\)
P/s: Lần sau cậu nên chia nhỏ ra đăng nhé!
a) 192=(20-1)2=202-2.20.1+12=400-40+1=361;
282=(30-2)2=302-2.30.2+22=900-120+4=784;
812=(80+1)2=802+2.80.1+12=6400+160+1=6561;
912=(90+1)2=902+2.90.1+12=8100+180+1=8281;
b) 19.21=(20-1)(20+1)=202-1=400-1=399;
29.31=(30-1)(30+1)=302-1=900-1=899;
39.41=(40-1)(40+1)=402-1=1600-1=1599
c) 292-82=(29-8)(29+8)=21.37=37(20+1)=740+37=777
562-462=(56-46)(56+46)=10.100=1000
672-562=(67-56)(67+56)=11.123=123(10+1)=1230+123=1353
a)
19^2=(20−1)^2=20^2−2.20.1+1^2=400−40+1=361
28^2=(30−2)^2=30^2−2.30.2+2^2=900−120+4=784
81^2=(80+1)^2=80^2+2.80.1+1^2=6400+160+1=6561
91^2=(90+1)^2=90^2+2.90.1+1^2=8100+180+1=8281
\(19^2=\left(20-1\right)^2=20^2-2.20.1+1^2=400-40+1=361\)
\(28^2=\left(30-2\right)^2=30^2-2.30.2+2^2=900-120+4=784\)
\(81^2=\left(80+1\right)^2=80^2+2.80.1+1^2=6400+160+1=6561\)
\(91^2=\left(90+1\right)^2=90^2+2.90.1+1^2=8100+180+1=8281\)
\(19.21=\left(20-1\right).\left(20+1\right)=20^2-1^2=400-1=399\)
\(29.31=\left(30-1\right).\left(30+1\right)=30^2-1^2=900-1=899\)
\(39.41=\left(40-1\right).\left(40+1\right)=40^2-1^1=1600-1=1599\)
\(29^2-8^2=\left(29-8\right).\left(29+8\right)=777\)
- 2 phần còn lại bạn cứ làm tương tự :) Vì mk bận nên chỉ giúp đc đến đây thoy <: Chúc bạn học tốt =)
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