giúp mình với , ( bài 30 Câu 1,2) Question giúp mình với , ( bài 30 Câu 1,2) in progress 0 Môn Toán Verity 4 years 2020-11-16T16:12:39+00:00 2020-11-16T16:12:39+00:00 2 Answers 88 views 0
Answers ( )
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
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`
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