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\(a,\left(6x+1\right)\left(x+2\right)-2x\left(3x-5\right)\)
\(=6x^2+12x+x+2-6x^2+10x\)
\(=23x+2\)
a) (6x + 1)(x + 2) - 2x(3x - 5)
= 6x2 + 12x + x + 2 - 6x2 + 10x
= (6x2 - 6x2) + (12x + x + 10x) + 2
= 23x + 2
b) (2x - 1)2 - (2x - 3)(2x + 3)
= 4x2 - 4x + 1 - 4x2 + 9
= (4x2 - 4x2) - 4x + (1 + 9)
= -4x + 10
c) (2x - 3)3 - (3x + 1)(5 - 4x) - 16x2
= 8x3 - 36x2 + 54x - 15x + 12x2 - 5 + 4x - 16x2
= 8x3 - (36x2 - 12x2 + 16x2) + (54x - 15x + 4x) - 5
= 8x3 - 40x2 + 43x - 5
d) (3x + 2) - (x - 5) - x(3x - 13)
= 3x + 2 - x + 5 - 3x2 + 13x
= (3x - x + 13x) + (2 + 5) - 3x2
= 15x + 7 - 3x2
Bài 1:
a: \(A=3\left(x^2-2x+1\right)-\left(x^2+2x+1\right)+2\left(x^2-9\right)-\left(4x^2+12x+9\right)-5+20x\)
\(=3x^2-6x+3-x^2-2x-1+2x^2-18-\left(4x^2+12x+9\right)-5+20x\)
\(=4x^2-8x-16-5+20x-4x^2-12x-9\)
\(=-30\)
b: \(B=5x\left(x^2-49\right)-x\left(4x^2-4x+1\right)-\left(x^3+4x^2-246x\right)-175\)
\(=5x^3-245x-4x^3+4x^2-x-x^3-4x^2+246x-175\)
\(=-175\)
d: \(D=25x^2-20x+4-36x^2-12x-1+11\left(x^2-4\right)-48+32x\)
\(=-11x^2-32x+3-48+32x+11x^2-44\)
=-89
a. gọi phần đầu đấy là A nhá, để đỡ cần viết lại
A=...............
= (3x+5)2 + ( 3x-5)2 - 9x2 -4
= (9x2 +30x + 25 ) + ( 9x2 -30x+ 25 ) - 9x2 -4
= 9x2 +30x + 25 + 9x2 -30x+25-9x2 -4
= 9x2 + 46
sai thì thôi nhé. bạn nên kiểm tra lại
d. (2x-1)*(4x2 + 2x +1 ) - 8x*( x2 +1) - 5
= 8x3 -1 - 8x3 -8x-5
= -8x-6
= -2(4x+3)
sai nhé. bạn nên kiểm tra lại
a) \(=\left[\left(6x+1\right)+\left(6x-1\right)\right]^2\)
\(=\left(12x\right)^2\)
\(=144x^2\)
$(6x+1)^2+(6x-1)^2-2(1+6x)(6x-1)$
$=(6x+1)^2+(6x-1)^2-2(6x+1)(6x-1)$
$=[(6x+1)-(6x-1)]^2$
$=2^2$
$=4$
b)$3(2^2-1)(2^4+1)(2^8+1)(2^{16}+1)$
$=3(2^2-1)(2^4+1)(2^8+1)(2^{16}+1)$
$=3(2^2-1)\cdot\dfrac{2^8-1}{2^4-1}\cdot\dfrac{2^{16}-1}{2^8-1}\cdot\dfrac{2^{32}-1}{2^{16}-1}$
$=3(2^2-1)\cdot\dfrac{2^{32}-1}{2^4-1}$
$=3\cdot\dfrac{2^{32}-1}{2^2+1}$
$=\dfrac{3(2^{32}-1)}{5}$
$\textbf{1)}$
$(4x-1)^2-2(4x-1)(3x-7)+(7-3x)^2$
$=(4x-1)^2-2(4x-1)(3x-7)+(3x-7)^2$
$=\left[(4x-1)-(3x-7)\right]^2$
$=(x+6)^2.$
Tại $x=44$: $(44+6)^2=50^2=2500.$
$\textbf{2)}$
$(2x-5)^2-2(2x-5)(3x-4)+(4-3x)^2$
$=(2x-5)^2-2(2x-5)(3x-4)+(3x-4)^2$
$=\left[(2x-5)-(3x-4)\right]^2$
$=(x+1)^2.$
Tại $x=24$: $(24+1)^2=625.$
a: Đặt \(C=3\left(x-1\right)^2-\left(x+1\right)^2+2\left(x-3\right)\left(x+3\right)-\left(2x+3\right)^2-\left(5-20x\right)\)
\(D=5x\left(x-7\right)\left(x+7\right)-x\left(2x-1\right)^2-\left(x^3+4x^2-246x\right)-175\)
Do đó: A=C+D
\(C=3\left(x-1\right)^2-\left(x+1\right)^2+2\left(x-3\right)\left(x+3\right)-\left(2x+3\right)^2-\left(5-20x\right)\)
\(=3x^2-6x+3-x^2-2x-1+2x^2-18-\left(4x^2+12x+9\right)-5+20x\)
\(=4x^2-8x-16-4x^2-12x-9-5+20x\)
\(=-30\)
\(D=5x\left(x-7\right)\left(x+7\right)-x\left(2x-1\right)^2-\left(x^3+4x^2-246x\right)-175\)
\(=5x\left(x^2-49\right)-x\left(4x^2-4x+1\right)-x^3-4x^2+246x-175\)
\(=5x^3-245x-4x^3+4x^2-x-x^3-4x^2+246x-175\)
=-175
A=C+D=-30-175=-205
b: Đặt \(E=-2x\left(3x+2\right)^2+\left(4x+1\right)^2+2\left(x^3+8x^2+3x-2\right)-\left(5-x\right)\)
\(F=\left(5x-2\right)^2-\left(6x+1\right)^2+11\left(x-2\right)\left(x+2\right)-16\left(3-2x\right)\)
Do đó: B=E+F
\(E=-2x\left(3x+2\right)^2+\left(4x+1\right)^2+2\left(x^3+8x^2+3x-2\right)-\left(5-x\right)\)
\(=-2x\left(9x^2+12x+4\right)+16x^2+8x+1+2x^3+16x^2+6x-4-5+x\)
\(=-18x^3-24x^2-8x+32x^2+14x+1-5+x\)
\(=-18x^3+8x^2+7x-4\)
\(F=\left(5x-2\right)^2-\left(6x+1\right)^2+11\left(x-2\right)\left(x+2\right)-16\left(3-2x\right)\)
\(=25x^2-20x+4-36x^2-12x-1+11x^2-44-48+32x\)
\(=-95\)
\(B=-18x^3+8x^2+7x-99\)
Bài 2:
a: Ta có: \(A=\left(x+1\right)^3+\left(x-1\right)^3\)
\(=x^3+3x^2+3x+1+x^3-3x^2+3x-1\)
\(=2x^3+6x\)
b: Ta có: \(B=\left(x-3\right)^3-\left(x+3\right)\left(x^2-3x+9\right)+\left(3x-1\right)\left(3x+1\right)\)
\(=x^3-9x^2+27x-27-x^3-27+9x^2-1\)
\(=27x-55\)
Ta có:
$(x+4)^2-x^2(x+12)=16$
$x^2+8x+16-x^3-12x^2=16$
$-x^3-11x^2+8x=0$
$-x(x^2+11x-8)=0$
Suy ra:
$x=0$ hoặc $x^2+11x-8=0$
Giải phương trình bậc hai:
$x=\dfrac{-11\pm\sqrt{121+32}}{2}$
$=\dfrac{-11\pm\sqrt{153}}{2}$
$=\dfrac{-11\pm3\sqrt{17}}{2}$
Vậy: $x=0,\quad x=\dfrac{-11+3\sqrt{17}}2,\quad x=\dfrac{-11-3\sqrt{17}}2$
Ta có:
$(x+3)^3=x^3+9x^2+27x+27$
$x(3x+1)^2=x(9x^2+6x+1)=9x^3+6x^2+x$
$(2x+1)(4x^2-2x+1)=8x^3+1$
Do đó:
$x^3+9x^2+27x+27-9x^3-6x^2-x+8x^3+1=28$
$3x^2+26x+28=28$
$3x^2+26x=0$
$x(3x+26)=0$
Suy ra: $x=0\text{ hoặc }x=-\dfrac{26}{3}$
Nhận thấy: $(x+5)(x^2-5x+25)=x^3+125$
Do đó: $(x-2)^3-x^3-125-6x^2=11$
$x^3-6x^2+12x-8-x^3-125-6x^2=11$
$-12x^2+12x-133=11$
$-12x^2+12x-144=0$
$-12(x^2-x+12)=0$
$x^2-x+12=0$
Có: $\Delta=(-1)^2-4\cdot1\cdot12=-47<0$
Vậy phương trình không có nghiệm thực