= x³ - (31 -1)x² - 31x + 1

Thay x = 31, ta được

x³ - (x-1)x² - x² + 1

= x³ - x³ + x² - x² +1 

= 1

Vậy gái trị của biểu thức đã cho tại x = 31 là 1

31 x 15 x 7² x 4 - 31 x 49 x 40

 = 31 x 15 x 49 x 4 - 31 x 49 x 4 x 10

= 31 x 49 x 4 x ( 15 - 10)

= 31 x 49 x 4 x 5

...

31 x 15 x 7^2 x 4 - 31 x 49 x 40

= 31 x 15 x 49 x 4 - 31 x 46 x 40

= 31 x 49 x ( 15 x 4 - 40 )

= 31 x 49 x 20

= 30380

31 x 15 x 7² x 4 - 31 x 49 x 40

= 1860 x 49 - 1240 x 49

= (1860 - 1240) x 49

= 620 x 49

= 30380

Tính nhanh:

a, 35x18 -5.7x28 = 35x18 -35x28 = 35 x (18 – 28) = 35 x ( -10) = -350

b,24x(16-5)-16x(24-5) = 24x16 – 24 x 5- 16x24 + 16x5 = (– 24 + 16)x 5 = -8 x 5 = -40

d,31x(-18)+31x(-81)-31 = 31x (-18  -81 – 1) =  31 x (-100) = -3100

e,(-12)x47+(-12)x52+(-12) = (-12)x (47+52 + 1)= (-12)x 100= - 1200

Ý c chưa rõ đề bài...

\(a.35\times18-5.7\times28\)

\(=35.18-35.28\)

\(=35.\left(18-28\right)\)

\(=35.\left(-10\right)\)

\(=-350\)

\(b.24.\left(16-5\right)-16.\left(24-5\right)\)

\(=24.16-24.5-16.24-16.5\)

\(=\left(24.16-16.24\right)-24.5-16.5\)

\(=0-\left(24+16\right).5\)

\(=0-40.5\)

\(=0-200\)

\(=-200\)

Ôi sr bn, câu b tớ nhầm dấu

= 31.(-18 - 81 - 1)
= 31 . ( - 100 )
= -3100

\(31.\left(-18\right)+31\left(-81\right)-31\)

\(=31\left(-18-81-1\right)\)

\(=31\left(-100\right)\)

\(=-3100\)

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\(=0,25\times49+0,25+0,25\times31+0,25\times19\\ =0,25\times\left(49+1+31+19\right)\\ =0,25\times100\\ =25\)

`25%×49+25/100+1/4×31+0,25×19`

`=0,25×49+0,25+0,25×31+0,25×19`

`=0,25×(49+1+31+19)`

`=0,25×100`

`=25`

\(25\%\times49+\dfrac{25}{100}+\dfrac{1}{4}\times31+0,25\times19\)

\(=\dfrac{25}{100}\times49+\dfrac{25}{100}+\dfrac{1}{4}\times31+\dfrac{1}{4}\times19\)

\(=\dfrac{1}{4}\times49+\dfrac{1}{4}+\dfrac{1}{4}\times31+\dfrac{1}{4}\times19\)

\(=\dfrac{1}{4}\times\left(49+31+19\right)\)

\(=\dfrac{1}{4}\times100\)

\(=25\)

\(P=x^3+31x^2-x^2-31x+1=\left(x+31\right)\left(x^2-1\right)+1\)

thay x=31 vào rồi tính thôi nha

Đề không saiA=313−30.312−31.31+1 =31.312−30.312−312+1=312(31−30−1)+1=312.0+1A=1

5/3

1/3

2/3

3/2

5/3

1/3

2/3

3/2

\(1+\dfrac{2}{3}=\dfrac{3}{3}+\dfrac{2}{3}=\dfrac{5}{3}\)

\(1-\dfrac{2}{3}=\dfrac{3}{3}-\dfrac{2}{3}=\dfrac{1}{3}\)

\(1\times\dfrac{2}{3}=\dfrac{2}{3}\)

\(1\div\dfrac{2}{3}=1\times\dfrac{3}{2}=\dfrac{3}{2}\)