∵(5n+2)(5n+3)-6
=25n²+10n+15n+6-6
=25n²+25n
=25n(n+1)
n是正整数时,25乘以两个连续的两个整数肯定是50的倍数
所以若n是正整数,则代数式(5n+2)(5n+3)-6的值是50的倍数是真命题