数学一题

freebenben

DS我：what is the remainder when 3^(4x+y)+y is divided by 10?
1:x=25
2:y=1
the confirmed answer is B, could someone tell me how to work it out? Thank you!

cook

I am not sure the expression: 3^(4x+y)+y : means{ 3^(4x+y)}+y or 3^{(4x+y)+y},

But the way to solve the problem is : 1. if you know n , the remainder of 3^n divided by 10 will clear, and moreover, unit digit of 3^4x = 1 . 2. from above: n=4x+y or n=4x+2y , those express can be changed to 3^4x*3^y or 3^4x*3^2y .

So, once you know y, you will know the answer to this question.

freebenben

got you, thank you very much. I believe the right expression is the former one. thanks again.