Question

[Pham Bang Bang]

A=5+5²+5³+.......+5¹⁰⁰

a)Chung to A:6

b)chung to A:13

c)tim x thuoc N sao cho 4A+5=5^x+2

^{d)4A+5 phai la so chinh phuong khong}

^{giup minh voi minh dang can gap}

^{cam on cac ban}

Answer 1

[hoanggibao796]

cau nay kho qua bang a

Answer 2

[minh man]

A=5+5²+5³+...+5¹⁰⁰ = (5+5²)+(5³+5⁴)+...+(5⁹⁹+5¹⁰⁰)

A=(5+5²)+5².(5+5²)+5⁴.(5+5²)+...+5⁹⁸.(5+5²)

A=30+30.5²+30.5⁴+...+30.5⁹⁸ = 30.(1+5²+5⁴+...+5⁹⁸)\(⋮\)30

=>A\(⋮\)6