Bài 5

a) A = -x³ + 6x² - 12x + 8

= -x³ + 3.(-x)².2 - 3.x.2² + 2³

= (-x + 2)³

= (2 - x)³

Thay x = -28 vào A ta được:

A = [2 - (-28)]³

= 30³

= 27000

b) B = 8x³ + 12x² + 6x + 1

= (2x)³ + 3.(2x)².1 + 3.2x.1² + 1³

= (2x + 1)³

Thay x = 1/2 vào B ta được:

B = (2.1/2 + 1)³

= 2³

= 8

Bài 6

a) 11³ - 1 = 11³ - 1³

= (11 - 1)(11² + 11.1 + 1²)

= 10.(121 + 11 + 1)

= 10.133

= 1330

b) Đặt B =  x³ - y³ = (x - y)(x² + xy + y²)

= (x - y)(x² - 2xy + y² + 3xy)

= (x - y)[(x - y)² + 3xy]

Thay x - y = 6 và xy = 9 vào B ta được:

B = 6.(6² + 3.9)

= 6.(36 + 27)

= 6.63

= 378

Bài 6 :

a) \(11^3-1=\left(11-1\right)\left(11^2+11+1^2\right)\)

\(\)\(=10.\left(121+12\right)\)

\(=10.133\)

\(=1330\)

b) \(\left\{{}\begin{matrix}x-y=6\\xy=9\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x^2+y^2-2xy=36\\xy=9\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x^2+y^2-2.18=36\\xy=9\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x^2+y^2=72\\xy=9\end{matrix}\right.\)

Ta có :

\(x^3-y^3=\left(x-y\right)\left(x^2+y^2+xy\right)\)

\(=6.\left(72+9\right)\)

\(=6.81\)

\(=486\)

a, ( -18 + 25 ) - ( 125 - 18 + 25 )

= -18+25-125+18-25

= (-18+18) +(25-25) -125

= 0+0-125

= -125

b, 45 . ( 18 - 15 ) -18 . ( 45 + 45 )

= 45.18 - 45.15 -18.45 +18.45

= 45(18-15-18+18)

= 45.3=135

a ) = -18 + 25 - 125 + 18 - 25

= (-18 + 18 ) - ( 25 -25 ) + 125

= 0              -    0            + 125

=125

113.37+226.17-13.71=4181+3842-923=8023-923=7100

bn nhớ cho mik nha mik lại cho.

bằng 325.83

nha bn

k mk nha bn

thanks

a, 21.35-3.25.7=21.35-21.25=21.(35-25)=21.10=210

b, 77-11.(30+7)=77-330-77=-330

c, 85.(35-27)-35.(85-27)=85.35-85.27-35.85+35.27=0

d, 47.(45-15)-47.(45+15)=47.45-47.15-47.45-47.15=-2(47.15)=1410

a, 21.35-3.25.7=21.35-21.25=21.10=210

b,77-11.(30+7)=77-11.30-11.7=-11.30=-330

c,85.(35-27)-35.(85-27)=85.35-85.27-85.35+35.27=27.(-50)=-1350

d, 47.(45-15)-47.(45+15)=47.45-47.15-47.45-47.15=-47.30=-1410

a, 21 . 35 - 3 . 25 . 7

= (21 . 35) - (3 . 25 . 7)

= 735 - 525

= 210

b, 77-11.(30+7)

= 77 - 11.30 - 11.7

= -11.30

= -330

c, 85.(35-27)-35.(85-27)

= 85.35 - 85.27 - 85.35 + 35.27

= 27.(-50)

= -1350

d, 47.(45-15)-47.(45+15)

= 47.45 - 47.15 - 47.45 - 47.15

= -47.30

= -1410

a) 2.5³-3.2+4⁵:4³
= 2.125-6+16
= 250+10
= 260

250-6 + 4^5-3 =>250-6 + 4² =>250-6 + 16 =>260

=260

a,[(-18)+(-17)+10]-(-18)

=-18-17+10+18

=(-18+18)+(-17+10)

=0-7

=-7

b,(-11+14).(-3+7)

=-11.(-3)+(-11).7+14.(-3)+14.7

=33+(-77)+(-42)+98

=(33+98)+[-77+(-42)]

=131-119

=12

c,45.(-10)+3.15.(-2)+2.45

=45.[(-10)+3.(-2)+2]

=45.-14

=-630

a) \(\text{ }\left[\left(-18\right)+\left(-17\right)+10\right]-\left(-18\right)\)

\(=\text{ }\left[\left(-18\right)+\left(-17\right)+10\right]+18\)

\(=\left(-18\right)+\left(-17\right)+10+18\)

\(=\text{ }\left[\left(-18\right)+18\right]+\text{ }\left[\left(-17\right)+10\right]\)

\(=0+\left(-7\right)\)

\(=-7\)

b) (-11+ 14) . (-3+7)

= 3 . 4

= 12

\(a\frac{31}{23}-\left(\frac{7}{23}+\frac{8}{23}\right)\)

\(=\frac{31}{23}-\frac{7}{23}-\frac{8}{23}\)

\(=\frac{16}{23}\)

Hot

tốt

!

a)\(\frac{31}{23}-\left(\frac{7}{23}+\frac{8}{23}\right)=\frac{31}{23}-\frac{8}{23}+\frac{7}{23}=1+\frac{7}{23}=1\frac{7}{23}\)

b)\(\left(\frac{1}{3}+\frac{12}{67}+\frac{13}{41}\right)-\left(\frac{79}{67}-\frac{28}{41}\right)=\left(\frac{13}{41}+\frac{28}{41}\right)+\left(\frac{79}{67}-\frac{12}{67}\right)-\frac{1}{3}=1+1-\frac{1}{3}\)

\(=2-\frac{1}{3}=\frac{5}{3}\)