79、If x and y are positive integers,what is the remainder when 3^(4+4x)+9^y is divided by 10? (1)x=25 (2)y=1 the answer is b myself answer is d, their have some reasons: 1.3^(4+4x)+9^y=3^[8y(1+x)] 2.because 3 is 4个数一个来回,即3。9。7。1 这样的,所以把1。2的条件带入都是可以得的 说不清了,但是请NN给个答案,我看了讨论贴,没它的讨论。。。。谢谢 |