Sửa đề: Tính \(x^4-y^4\)
Ta có: \(x+y=-1\)
\(\Leftrightarrow\left(x+y\right)^2=1\)
\(\Leftrightarrow x^2+2xy+y^2=1\)
\(\Leftrightarrow25+2xy=1\)
\(\Leftrightarrow2xy=-24\)
Ta có: \(\left(x-y\right)^2\)
\(=x^2-2xy+y^2\)
\(=25+24=49\)
\(\Leftrightarrow x-y=7\)
Ta có: \(x^4-y^4\)
\(=\left(x^2+y^2\right)\left(x^2-y^2\right)\)
\(=\left(x^2+y^2\right)\left(x-y\right)\left(x+y\right)\)
\(=25\cdot7\cdot\left(-1\right)=-175\)
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