\(A=x^3-y^3-21xy\)
\(A=\left(x-y\right).\left(x^2+xy+y^2\right)-21xy\)
\(A=7.\left(x^2+xy+y^2\right)-21xy\)
\(A=7.\left(x^2+xy+y^2+3xy\right)\)
\(A=7.\left(x^2+2xy+y^2+2xy\right)\)
\(A=7.\text{[}\left(x+y\right)^2+2xy\text{]}\)
\(A=7.\left(7^2+2xy\right)\)
\(A=7^3+14xy\)
Ngáo rồi @@
\(\)
\(A=x^3-y^3-21xy\)
\(\Rightarrow A=\left(x-y\right)\left(x^2+xy+y^2\right)-21xy\)
\(\Rightarrow A=7\left(x^2+xy+y^2\right)-21xy\)
\(\Rightarrow A=7\left(x^2+xy+y^2-3xy\right)\)
\(\Rightarrow A=7\left(x^2+y^2-2xy\right)\)
\(\Rightarrow A=7\left(x-y\right)^2\)
\(\Rightarrow A=7.7^2\)
\(\Rightarrow A=7.49\)
\(\Rightarrow A=343\)
\(B=x^3-3xy\left(x-y\right)-y^3-x^2+2xy-y^2\)
\(\Rightarrow B=\left(x^3-y^3\right)-3xy\left(x-y\right)-\left(x^2-2xy+y^2\right)\)
\(\Rightarrow B=\left(x-y\right)\left(x^2+xy+y^2\right)-21xy-\left(x-y\right)^2\)
\(\Rightarrow B=7\left(x^2+xy+y^2\right)-21xy-7^2\)
\(\Rightarrow B=7\left(x^2+xy+y^2-3xy\right)-49\)
\(\Rightarrow B=7\left(x^2+y^2-2xy\right)-49\)
\(\Rightarrow B=7\left(x-y\right)^2-49\)
\(\Rightarrow B=7.7^2-7^2\)
\(\Rightarrow B=7^2\left(7-1\right)\)
\(\Rightarrow B=49.6\)
\(\Rightarrow B=294\)
\(C=x^2\left(x+1\right)-y^2\left(y-1\right)+xy-3xy\left(x-y+1\right)-95\)
\(\Rightarrow C=x^3+x-y^3+y+xy-3xy\left(7+1\right)-95\)
\(\Rightarrow C=\left(x^3-y^3\right)+x+y+xy-3xy.8-95\)
\(\Rightarrow C=\left(x-y\right)\left(x^2+xy+y^2\right)+x+y+xy-24xy-95\)\(\Rightarrow C=7\left(x^2+xy+y^2\right)+x+y-23xy-95\)
\(\Rightarrow C=7\left(x^2+xy+y^2\right)-21xy+x+y-2xy-95\)
\(\Rightarrow C=7\left(x^2+xy+y^2-3xy\right)+\left(x-y\right)^2-95\)
\(\Rightarrow C=7\left(x^2+y^2-2xy\right)+\left(x-y\right)^2-95\)
\(\Rightarrow C=7\left(x-y\right)^2+7^2-95\)
\(\Rightarrow C=7.7^2+7^2-95\)
\(\Rightarrow C=7^2\left(7+1\right)-95\)
\(\Rightarrow C=49.8-95\)
\(\Rightarrow C=392-95\)
\(\Rightarrow C=297\)
