a) \(67\cdot73=\left(70-3\right)\left(70+3\right)=70^2-3^2=4900-9=4891\)
b) \(45^2+90\cdot55+55^2=45^2+2\cdot45\cdot55+55^2=\left(45+55\right)^2=100^2=10000\)
c) \(35\cdot48+350\cdot5,2=35\cdot48+35\cdot52=35\left(48+52\right)=35\cdot100=3500\)
B) \(45^{n+1}+45^n=45^n\left(45+1\right)=45^n\cdot46\)
Vì \(45^n \in \mathbb N \Rightarrow 45^n \times 46 \in \mathbb N \) \(\Rightarrow45^n\times46⋮46\)
hay \(\left(45^{n+1}+45^n\right)⋮46\)
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