Cho a. b, c > 0 . Chung minh rang : 4/a + 5/b + 3/c >= 4(3/a+b + 2/b+c + 1/c+a)
Biet so tu nhien a chia cho 5 du 4. Chung minh rang a2 chia cho 5 du 1.
cho ak=1-4/(ak+1)2. Chung minh rang T=a1a2a3...a50>1/3
chung minh rang 5^n-1-5^n chia hết cho 4 số tự nhiên n
chung minh rang 1/2^2+ 1\42 +1\62+1\82+ .......+1\(2.n)2<1\2
chung minh rang voi moi n thuoc N* thi 1^3+2^3+3^3+...+n^3= (1+2+3+...+n)^3
BAI 1: TIM X BIET so tu nhien x/7 du 6. chung minh rang x.x/7 du 1
bai 2: cho 2.(a.a+b.b)=(a+b).(a+b) chung minh rang a=b
cho f(x) = ax^3 + bx^2 +cx, f(x) - F(x-1) = x^2. chung minh rang 1^2 + 2^2 + 3^2+...+n^2 = (n(n+1)(2n+1))/6
cho a la so nguyen to lon hon 5.chung minh rang a4-1 chia het cho 240