Question

Ai giúp mình lm bài này vs ạ!!! Đúng mk tick cho =)))

Áp dụng các hằng đẳng thức đáng nhớ để thực hiện phép tính.

a, 19² ; 28² ; 81² ; 91²

b, 19.21 ; 29.31 ; 39.41

c, 28² - 8² ; 56² - 46² ; 67² - 57²

Answer 1

\(a,19^2=\left(18+1\right)^2=18^2+2.18.1+1^2=324+36+1=361\)

\(28^2=\left(27+1\right)^2=27^2+2.27.1+1^2=729+54+1=784\)

\(81^2=\left(80+1\right)^2=80^2+2.80.1+1^2=6400+160+1=6561\)

\(91^2=\left(90+1\right)^2=90^2+2.90.1+1^2=8100+180+1=8281\)

\(b,19.21=\left(20-1\right)\left(20+1\right)=20^2-1^2=400-1=399\)

\(29.31=\left(30-1\right)\left(30+1\right)=30^2-1^2=900-1=899\)

\(39.41=\left(40-1\right)\left(40+1\right)=40^2-1^2=1600-1=1599\)

\(c,28^2-8^2=\left(28-8\right)\left(28+8\right)=20.36=720\)

\(56^2-46^2=\left(56-46\right)\left(56+46\right)=10.102=1020\)

\(67^2-57^2=\left(67-57\right)\left(67+57\right)=10.124=1240\)

Answer 2

a) \(19^2=\left(20-1\right)^2=20^2-2.20.1+1^2=400-40+1=361\)

\(28^2=\left(30-2\right)^2=30^2-2.30.2+2^2=900-120+4=784\)

\(81^2=\left(80+1\right)^2=80^2+2.80.1+1^2=6400+160+1=6561\)

\(91^2=\left(90+1\right)^2=90^2+2.90.1+1^2=8100+180+1=8281\)