a) 3.|x-1|=27 b)|-2x+5|+8=21 Bài 2: Viết số (-15) thành tổng của hai số nguyên a) Cùng dấu b) Khác dấu có giá trị tuyệt đối nhỏ hơn 20 Bài 3 : a) Chứng minh : A= 3^1 + 3^2+3^3+3^4+....+3^2010 chia hết cho 3 và 13 b) Chứng minh : B=5¹+5²+5³+5⁴+....5^2010 chia hết cho 6 và 31 c) Chứng minh : C=7^1 + 7^2+7^3+7^4+....+7^2010 chia hết cho 8 và 57 Giúp mik nha ~~ Thank U

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