Question

Cho A=999993¹⁹⁹⁹ - 555557¹⁹⁹⁷. Chứng minh rằng:A chia hết cho 5 

Answer 1

999993¹⁹⁹⁶.999993³-5-555557¹⁹⁹⁶.555557=......1....7-.....1.....7=....7-...7=...0 tan cung la 0 nen chia het cho5

 

Answer 2

999993¹⁹⁹⁹=999993^4k+3=999993^4k.999993³=1.7=7(mod 10)
555557¹⁹⁹⁷=555557^4k+1=555557^4k.555557=1.7=7(mod 10)
ta có : A=999993¹⁹⁹⁷-555557¹⁹⁹⁷=7-7=0(mod 10)
hay A chia hết cho 5