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\(19^2=\left(20-1\right)^2=20^2-2.20+1=400-40+1=361\)
\(28^2=\left(30-2\right)^2=30^2-2.30.2+2^2=900-120+4=784\)
\(82^2=\left(80+2\right)^2=80^2+2.80.2+2^2=6400+2.80.2+4=6724\)
\(91^2=\left(90+1\right)^2=90^2+2.90.1+1^2=8100+180+1=8281\)
\(19.21=\left(20-1\right)\left(20+1\right)=20^2-1=400-1=399\)
\(39.41=\left(40-1\right)\left(40+1\right)=40^2-1=1600-1=1599\)
a) \(56^2+44^2+2.56.44=56^2+2.56.44+44^2=\left(56+44\right)^2=100^2=10000\)
b) \(36^2+64^2+72.64=36^2+2.36.64+64^2=\left(36+64\right)^2=100^2=10000\)
c) \(136^2+36^2-72.136=136^2-2.36.136+36^2=\left(136-36\right)^2=100^2=10000\)
a) $56^2+44^2+2.56.44=56^2+2.56.44+44^2=\left(56+44\right)^2=100^2=10000$562+442+2.56.44=562+2.56.44+442=(56+44)2=1002=10000
b) $36^2+64^2+72.64=36^2+2.36.64+64^2=\left(36+64\right)^2=100^2=10000$362+642+72.64=362+2.36.64+642=(36+64)2=1002=10000
c) $136^2+36^2-72.136=136^2-2.36.136+36^2=\left(136-36\right)^2=100^2=10000$
852+752+652+552−452−352−252-152
=(852-152)+(752-252)+(652-352)+(552-452)
=70.100+50.100+30.100+10.100
=160.100=16000
Sai ở chỗ:<=> 4-9/2 = 5-9/2 <=> 4=5
thế này mới đúng!
\(\left(4-\frac{9}{2}\right)^2=\left(5-\frac{9}{2}\right)^2\Leftrightarrow\left(4-\frac{9}{2}\right)\left(4-\frac{9}{2}\right)=\left(5-\frac{9}{2}\right)\left(5-\frac{9}{2}\right)\)