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

\(\frac{1}{27}-64+3=-\frac{80}{27}+3=\frac{1}{27}.\)

dẽ mk

học ngu  161/27

xl tui tính nhầm

mk pn cx ngu mk

kq phải =-1646/27

Trả lời

2002 x 1006

= ( 1504 + 498 ) x ( 1504 - 498 )

= 1504² - 498²

= 2014012

198 x 202 

= ( 200 - 2 ) x ( 200 + 2 )

= 202² - 2²

= 40800

\(=\left(3x\right)^2-2\cdot3x\cdot4+4^2-1\)

\(=\left(3x-4\right)^2-1^2\)

\(=\left(3x-4-1\right)\left(3x-4+1\right)\)

\(=\left(3x-5\right)\left(3x-3\right)\)

`1)(a^[1/4]-b^[1/4])(a^[1/4]+b^[1/4])(a^[1/2]+b^[1/2])`

`=[(a^[1/4])^2-(b^[1/4])^2](a^[1/2]+b^[1/2])`

`=(a^[1/2]-b^[1/2])(a^[1/2]+b^[1/2])`

`=a-b`

`2)(a^[1/3]-b^[2/3])(a^[2/3]+a^[1/3]b^[2/3]+b^[4/3])`

`=(a^[1/3]-b^[2/3])[(a^[1/3])^2+a^[1/3]b^[2/3]+(b^[2/3])^2]`

`=(a^[1/3])^3-(b^[2/3])^3`

`=a-b^2`

x³+64=x³+4³=(x+4)(x²-4x+4²)=(x+4)(x²-4x+16)

\(x^3+64=x^3+4^3=(x+4)(x^2-3x+16)\)

\(299.301=\left(300-1\right)\left(300+1\right)=300^2-1^2=90000-1=89999\)

\(299\cdot301=300^2-1=89999\)