Question

[gay phan]

5) tinh nhanh :

a) 301² b) 499² c) 68*72

Answer 1

[Trần Quốc Lộc]

\(\text{a) }301^2\\ =\left(300+1\right)^2\\ =300^2+2\cdot300\cdot1+1^2\\ =90000+600+1\\ =90601\\ \)

\(\text{b) }499^2\\ =\left(500-1\right)^2\\ =500^2-2\cdot500\cdot1+1^2\\ =250000-1000+1\\ =249001\\ \)

\(\text{c) }68\cdot72\\ =\left(70-2\right)\left(70+2\right)\\ =70^2-2^2\\=4900-4\\ =4896\\ \)

Answer 2

[Đời về cơ bản là buồn... cười!!!]

a) \(301^2\)

\(=\left(300+1\right)^2\)

\(=300^2+600+1\)

\(=90601\)

b) \(499^2\)

\(=\left(500-1\right)^2\)

\(=500^2-1000+1\)

\(=249001\)

c) \(68\cdot72\)

\(=\left(70-2\right)\left(70+2\right)\)

\(=70^2-2^2\)

\(=4896\)