giúp mình với , ( bài 30 Câu 1,2)

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giúp mình với , ( bài 30 Câu 1,2)
giup-minh-voi-bai-30-cau-1-2

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Verity 4 years 2020-11-16T16:12:39+00:00 2 Answers 86 views 0

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    0
    2020-11-16T16:13:39+00:00

    Bài 30

    1)(x+5)³-15x(x+10)

    =x³+15x²+75x+125-15x²-150x

    =x³-75x+125

    2)(x-2)³-(x-5)²

    =x³-6x²+12x-8-x²+10x-25=x³-7x²+22x-33

    3)(x+2)(x²-2x+4)-(x³+8)

    =(x³+8)-(x³+8)=0

    4)(x-3)(x²+3x+9)-(x²-1)(x+27)

    =x³-27-x³+x-27x²+27=x-27x²

    5)(3-x)³-(x+3)(x²-3x+9)

    =27-27x+9x²-x³-x³-27=-27x+9x²

    6)(x-2)(x²+2x+4)-x(x-3)(x+3)

    =x³-8-x²+9x

    Bài 31

    1)(x+3)(x-4)+(x-4)²

    =x²-x-12+x²-8x+16=2x²-9x+4=(x-4)(2x-1)

    2)(x-2)³-(3+x²)(3-x)

    =x³-6x²+12x-8-9-3x²+3x+x³

    =2x³-9x²+15x-16

    3)x(x-14)-10(x-1)²

    =x²-14x-10x²+20x-10

    =-9x²+6x-10

    4)2x(x+2)-(x+2)(x-2)

    =(x+2)(2x-x+2)=(x+2)²

    0
    2020-11-16T16:14:05+00:00

    Đáp án:

     

    Giải thích các bước giải:

    Bài 30:

    1) `(x + 5)^3 – 15x(x + 10)`

    `= x^3 + 3.x^2 .5 + 3.x.5^2 + 5^3 – 15x^2 – 150x`

    `= x^3 + 15x^2 + 75x + 125 – 15x^2 – 150x`

    `= x^3 + (15x^2 – 15x^2) + (75x – 150x) + 125`

    `= x^3 – 75x + 125`

    2) `(x – 2)^3 – (x – 5)^2`

    `= x^3 – 3.x^2 .2 + 3.x.2^2 + 2^3 – (x^2 – 2.x.5 + 5^2)`

    `= x^3 – 6x^2 + 12x + 8 – x^2 + 10x – 25`

    `= x^3 + (-6x^2 – x^2) + (12x + 10x) – 25`

    `= x^3 – 7x^2 + 22x – 25`

    Học tốt. Nocopy

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