说明5的平方乘3的2n+1次方减2的n次方乘3的n次方乘6的n+2次方能被13整除
问题描述：
说明5的平方乘3的2n+1次方减2的n次方乘3的n次方乘6的n+2次方能被13整除
答
5^2×3^(2n+1)×2^n-3^n×6^(n+2)
=5^2×3^(2n+1)×2^n-3^n×(2×3)^(n+2)
=5^2×3^(2n+1)×2^n-3^n×2^(n+2)×3^(n+2)
=5^2×3^(2n+1)×2^n-3^(2n+2)×2^(n+2)
=5^2×3^(2n+1)×2^n-3^(2n+1)×3×2^n×2^2
=3^(2n+1)×2^n×[5^2-3×2^2]
=3^(2n+1)×2^n×[25-12]
=3^(2n+1)×2^n×13
可以看出,上式是13的倍数,所以它能被13整除.