## giúp mình với , ( bài 30 Câu 1,2)

Question

giúp mình với , ( bài 30 Câu 1,2)

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

1. 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

2. 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