Question

5×4+4×3+3×2+2×1简便运算？

Answer 1

我觉得这道题不需要简便运算，都是个位数的乘法，还有加法，应该是先做乘除，然后再做加减。
5×4+4×3+3×2+2×1
=20+12+6+2
=40

Answer 2

考察一般项第k项，k(k+1)=k²+k

1×2+2×3+3×4+...+n(n+1)

=(1²+2²+3²+...+n²)+(1+2+3+...+n)

=n(n+1)(2n+1)/6 +n(n+1)/2

=[n(n+1)/6](2n+1+3)

=n(n+1)(2n+4)/6

=⅓n(n+1)(n+2)

这里K＝4，答案是40

Answer 3

4/5乘以2/3+1/5除以3/2如何轻松计算4/5乘2/3+1/5乘以3/2=4/5倍2/3+1/5倍3=（4/5+1/3）乘以2/2=1/3=2/3

Answer 4

4/5乘以2/3+1/5除以3/2如何轻松计算4/5乘2/3+1/5乘以3/2=4/5倍2/3+1/5倍3=（4/5+1/3）乘以2/2=1/3=2/3

Answer 5

4/5乘以2/3+1/5除以3/2如何轻松计算4/5乘2/3+1/5乘以3/2=4/5倍2/3+1/5倍3=（4/5+1/3）乘以2/2=1/3=2/3