Question

算式3*1!-4*2!+5*3!-6*4!+7*5!-8*6!+9*7!的值为（）要有步骤

Answer 1

=(2+1)*1! -(3+1)*2! +(4+1)*3! -(5+1)*4! +(6+1)*5! -(7+1)*6! +(8+1) *7!

= (2! +1!) -(3!+2!) +(4!+3!) -(5!+4!) +(6!+5!) -(7!+6!) +(8!+7!)

= 1 +8!

= 40321