bài tìm x nha các bn: 3xy(x+y)-(x+y)(x ²+y ²+2xy)+y ³=27 LM 1 BÀI THUI NHA. MIK ĐANG CẦN GẤP Ạ 11/07/2021 Bởi Allison bài tìm x nha các bn: 3xy(x+y)-(x+y)(x ²+y ²+2xy)+y ³=27 LM 1 BÀI THUI NHA. MIK ĐANG CẦN GẤP Ạ
`3xy(x+y)-(x+y)(x²+y²+2xy)+y³=27` `⇔3x²y+3xy²-(x+y)(x+y)²+y³=27` `⇔3x²y+3xy²-(x+y)³+y³=27` `⇔3x²y+3xy²-(x³+3x²y+3xy²+y³)+y³=27` `⇔3x²y+3xy²-x³-3x²y-3xy²-y³+y³=27` `⇔-x³=27` `⇔x³=-27` `⇔x³=(-3)³` `⇔x=-3` Bình luận
Đáp án: `3xy (x + y) – (x + y) (x^2 + y^2 + 2xy) + y^3 = 27` $\\$ `⇔ 3xy . x + 3xy . y – [x . (x^2 + y^2 +2xy) + y . (x^2 + y^2 + 2xy)] + y^3 = 27` $\\$ `⇔ 3x^2y + 3xy^2 – [x^3 + xy^2 + 2x^2y + x^2y + y^3 + 2xy^2] + y^3 = 27` $\\$ `⇔ 3x^2y + 3xy^2 – x^3 – xy^2 – 2x^2y – x^2y – y^3 – 2xy^2 + y^3 = 27` $\\$ `⇔ (3x^2y – 2x^2y – x^2y) + (3xy^2 – 2xy^2 – xy^2) – x^3 + (-y^3 + y^3) = 27` $\\$ `⇔ -x^3 = 27` $\\$ `⇔ x^3 = -27` $\\$ `⇔ x^3 = -3^3` $\\$ `⇔ x = -3` $\\$ Vậy `x=-3` Bình luận
`3xy(x+y)-(x+y)(x²+y²+2xy)+y³=27`
`⇔3x²y+3xy²-(x+y)(x+y)²+y³=27`
`⇔3x²y+3xy²-(x+y)³+y³=27`
`⇔3x²y+3xy²-(x³+3x²y+3xy²+y³)+y³=27`
`⇔3x²y+3xy²-x³-3x²y-3xy²-y³+y³=27`
`⇔-x³=27`
`⇔x³=-27`
`⇔x³=(-3)³`
`⇔x=-3`
Đáp án:
`3xy (x + y) – (x + y) (x^2 + y^2 + 2xy) + y^3 = 27`
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`⇔ 3xy . x + 3xy . y – [x . (x^2 + y^2 +2xy) + y . (x^2 + y^2 + 2xy)] + y^3 = 27`
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`⇔ 3x^2y + 3xy^2 – [x^3 + xy^2 + 2x^2y + x^2y + y^3 + 2xy^2] + y^3 = 27`
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`⇔ 3x^2y + 3xy^2 – x^3 – xy^2 – 2x^2y – x^2y – y^3 – 2xy^2 + y^3 = 27`
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`⇔ (3x^2y – 2x^2y – x^2y) + (3xy^2 – 2xy^2 – xy^2) – x^3 + (-y^3 + y^3) = 27`
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`⇔ -x^3 = 27`
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`⇔ x^3 = -27`
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`⇔ x^3 = -3^3`
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`⇔ x = -3`
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Vậy `x=-3`