Câu 5: Tìm\(x\), biết: \(2x\left( {x – 5} \right) – x\left( {3 + 2x} \right) = 26\)
\(2x\left( {x – 5} \right) – x\left( {3 + 2x} \right) = 26\)
\(\eqalign{& 2{x^2} – 10x – 3x – 2{x^2} = 26 \cr & – 13x = 26 \cr & x = – 2 \cr} \)
Câu 1.1: Làm tính nhân
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\(2{x^2}\left( {5{x^3} – 4{x^2}y – 7xy + 1} \right)\)
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\(2{x^2}\left( {5{x^3} – 4{x^2}y – 7xy + 1} \right)\) \( = 10{x^5} – 8{x^4}y – 14{x^3}y + 2{x^2}\)
Câu 1.2: Rút gọn biểu thức
\(2x\left( {3{x^3} – x} \right) – 4{x^2}\left( {x – {x^2} + 1} \right) + \left( {x – 3{x^2}} \right)x\)
\(2x\left( {3{x^3} – x} \right) – 4{x^2}\left( {x – {x^2} + 1} \right) + \left( {x – 3{x^2}} \right)x\)
\( = 6{x^4} – 2{x^2} – 4{x^3} + 4{x^4} – 4{x^2} + {x^2} – 3{x^3} = 10{x^4} – 7{x^3} – 5{x^2}\)
