Lịch sử là nhũng gì đã diễn quá khứ

4x2+4y2+4xy>6y−4

⇔4x2+4xy+4y2−6y+4>0

⇔(4x2+4xy+y2)+(3y2−6y+3)+1>0

⇔(2x+y)2+3.(y2−2y+1)+1>0

⇔(2x+y)2+3.(y−1)2+1>0(luôn đúng)

⇒
4x2+4y2+4xy>6y-4

n chia hết cho 3 => n =3k (k ∈Z)
n(n+1) =3k (3k+1) =
nếu k le ; k =2t+1 (t ∈Z)
3k (3k+1) =3(2t+1 )[ (3.(2t+1) +1 ] =3(2t+1 )[6t+3 +1) =3.(2t+1 )[6t+4)
=3(2t+1 ).2.(3t+2) =6(2t+1 ) (3t+2) chia hết cho 6
nếu k chẵn ; k =2t (t ∈Z)
3k (3k+1) =6t (3k+1 ] = chia hết cho 6
=> n(n+1) chia hết cho 6 nếu n chia hết cho 3=> dpcm

n chia hết cho 3 => n =3k (k ∈Z)
n(n+1) =3k (3k+1) =
nếu k le ; k =2t+1 (t ∈Z)
3k (3k+1) =3(2t+1 )[ (3.(2t+1) +1 ] =3(2t+1 )[6t+3 +1) =3.(2t+1 )[6t+4)
=3(2t+1 ).2.(3t+2) =6(2t+1 ) (3t+2) chia hết cho 6
nếu k chẵn ; k =2t (t ∈Z)
3k (3k+1) =6t (3k+1 ] = chia hết cho 6
=> n(n+1) chia hết cho 6 nếu n chia hết cho 3=> dpcm

Second, we ought to set up more rubbish bins. For instance, we can put more rubbish bins in the school gate, in front of each building, or in the playground. Thereby, we can make the waste collection easier. In addition, we should plant more trees. To give an example, we can encourage students to plant trees or flowers in our school because this reduces CO2 and makes the air clean