Tính nhẩm
a) 19^2 ; 28^2 ; 81^2 ; 101^2
b) 19.21 ; 29.31 ; 39.41 ; 99.101
c) 56^2-46^2 ; 64^2-36^2
d) 25^2 ; 35^2 ; 45^2 ; 55^2 ... 95^2
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
\(a,19^2=\left(18+1\right)^2=18^2+2.18.1+1^2=324+36+1=361\)
\(28^2=\left(27+1\right)^2=27^2+2.27.1+1^2=729+54+1=784\)
\(81^2=\left(80+1\right)^2=80^2+2.80.1+1^2=6400+160+1=6561\)
\(91^2=\left(90+1\right)^2=90^2+2.90.1+1^2=8100+180+1=8281\)
\(b,19.21=\left(20-1\right)\left(20+1\right)=20^2-1^2=400-1=399\)
\(29.31=\left(30-1\right)\left(30+1\right)=30^2-1^2=900-1=899\)
\(39.41=\left(40-1\right)\left(40+1\right)=40^2-1^2=1600-1=1599\)
\(c,28^2-8^2=\left(28-8\right)\left(28+8\right)=20.36=720\)
\(56^2-46^2=\left(56-46\right)\left(56+46\right)=10.102=1020\)
\(67^2-57^2=\left(67-57\right)\left(67+57\right)=10.124=1240\)
a,19.21=(20-1)(20+1)=202-12=400-1=399
29.31=(30-1)(30+1)=302-12=900-1=899
39.41=(40-1)(40+1)=402-12=1600-1=1599
b) 35 x 24 + 35 x 76 +55 x 19 +55 x 91
= 35 x ( 24 + 76 ) + 55 x ( 19 + 91 )
= 35 x100 +55 x 100
= 100 x ( 55 + 35 )
= 90 x 100 =9 000
c) \(6\cdot25\cdot4+4\cdot19\cdot6-2\cdot14\cdot12\)
\(=24\cdot25+24\cdot19-24\cdot14\)
\(=24\left(25+19-14\right)\)
\(=24\cdot30=720\)
d) \(19\cdot64+76\cdot34\)
\(=76\cdot19+76\cdot34\)
\(=76\left(19+34\right)=76\cdot53=4028\)
a) 2 x 16 x 50 x 25
= ( 2 x 50 ) x ( 16 x 25 )
= 100 x 400
= 40 000
a,79.101=79.(100+1)
= 79.100 + 79
=7900 + 79 = 7979
b,(1999+2016)-1999 = 1999 - 1999 + 2016 = 0 + 2016 = 2016
c,81+250+19 =(81 + 19) + 250 = 100 + 250 = 350
d,165+79+135 =(165+135)+79=300+79=379
e,35.45+35.55=35.(45+55)
= 35.100
=3500
f,5.125.2.8=(5.2).(125.8)
= 10 . 1000
= 10 000
\(19^2=\left(20-1\right)^2=20^2-2.20+1=400-40+1=361\)
\(28^2=\left(30-2\right)^2=30^2-2.30.2+2^2=900-120+4=784\)
\(82^2=\left(80+2\right)^2=80^2+2.80.2+2^2=6400+2.80.2+4=6724\)
\(91^2=\left(90+1\right)^2=90^2+2.90.1+1^2=8100+180+1=8281\)
\(19.21=\left(20-1\right)\left(20+1\right)=20^2-1=400-1=399\)
\(39.41=\left(40-1\right)\left(40+1\right)=40^2-1=1600-1=1599\)