a) 17 + 15 + (-27)

= (17 - 27) + 15

= -10 + 15

= 5

b) 13.75 + 25.13 - 300

= 13.(75 + 26) - 300

= 13.100 - 300

= 1300 - 300

= 1000

c) 80 - (4.5² - 5.2³) + 2021⁰

= 80 - (4.25 - 5.8) + 1

= 80 - (100 - 40) + 1

= 80 - 60 + 1

= 20 + 1

= 21

Đề khó nhìn quá bạn ơi!

a) 13.7 + 7.7

= (13 + 7).7

= 20 . 7

= 140

b) 2³ . 2016 . 5²

= 8 . 2016 . 25

= 200 . 2016

= 403200

c) 3² . 15 - 5.9

= 9.15 - 5.9

= (15 - 5).9

= 10.9

= 90

d) 13 + 15 + ........... + 57 + 59

Áp dụng công thức tính dãy số ta có :

\(\frac{\left[\left(59-13\right):2+1\right].\left(59+13\right)}{2}=\frac{24.72}{2}=864\)

a) 13 . 7 + 7 . 7

= (13 + 7) . 7

= 20 . 7

= 140

b) 2³ . 2016 . 5²

= 8 . 2016 . 25

= ( 8 . 25 ) . 2016

= 200 . 2016

= 403200 

c) 3² . 15 - 5 . 9

= 9 . 15 - 45

= 9 . 15 - 15 . 3

= ( 9 - 3 ) . 15

= 6 . 15

= 90

d) 13 + 15 + ........ + 57 + 59

Dãy số trên có số số hạng là:

( 59 - 13 ) : 2 + 1= 24 ( số hạng )

Tổng của dãy số trên là:

( 59 + 13 ) x 24 : 2 = 864

MK lm bài 1:

\(\left(a-b\right)\left(a+b\right)=a^2+ab-ab-b^2=a^2-b^2\)

Bài 1:

\(\left(a-b\right)\left(a+b\right)=a^2+ab-ab-b^2\)

\(=a^2-b^2\)

Câu 9

a) 2/15 + (-3/5)

= 2/15 - 3/5

= 2/15 - 9/15

= -7/15

b) -5/7 + 3/7 . (-2/9)

= -5/7 - 2/21

= -15/21 - 2/21

= -17/21

c) 5/16 - (7/15 - 3/16) + 17/30

= 5/16 - 7/15 + 3/16 + 17/30

= (5/16 + 3/16) + (17/30 - 14/30)

= 1/2 + 1/10

= 5/10 + 1/10

= 6/10

= 3/5

\(a,\dfrac{2}{15}+\left(-\dfrac{3}{5}\right)\\ =\dfrac{2}{15}-\dfrac{3}{5}\\ =\dfrac{2}{15}-\dfrac{9}{15}\\ =-\dfrac{7}{15}\\ b,-\dfrac{5}{7}+\dfrac{3}{7}\times\left(-\dfrac{2}{9}\right)\\ =-\dfrac{5}{7}-\dfrac{2}{21}\\ =-\dfrac{15}{21}-\dfrac{2}{21}\\ =-\dfrac{17}{21}\\ c,\dfrac{5}{16}-\left(\dfrac{7}{15}-\dfrac{3}{16}\right)+\dfrac{17}{30}\\ =\dfrac{5}{16}-\dfrac{7}{15}+\dfrac{3}{16}+\dfrac{17}{30}\\ =\left(\dfrac{5}{16}+\dfrac{3}{16}\right)-\left(\dfrac{17}{15}+\dfrac{17}{30}\right)\\ =\dfrac{1}{2}-\dfrac{17}{10}\\ =\dfrac{5}{10}-\dfrac{17}{10}\\ =-\dfrac{6}{5}.\)

a)2.18.14+3.17.12+4.69.9
=(2.18).14+(12.3).17+(4.9).69
=36.14+36.17+36.69
=36.(14+17+69)
=36.100
=3600

b)1+(-3)+5+(-7)+9+(-11)+13+(-15)
=[1+(-3)]+[5+(-7)]+[9+(-11)]+[13+(-15)]
=(-2)+(-2)+(-2)+(-2)
=(-8)

\(\left[504-\left(5^2.8+70\right):3^3+6\right]:25\)

\(\left[504-\left(25.8+70\right):27+6\right]:25\)

\(\left[504-\left(200+70\right):27+6\right]:25\)

\(\left[504-270:27+6\right]:25\)

\(\left[504-10+6\right]:25\)

\(\left[494+6\right]:25\)

\(500:25\)

= 20

\(\left[504-(5^2\cdot8+70):3^3+6\right]:25\)

\(=\left[504-(25\cdot8+70):27+6\right]:25\)

\(=\left[504-(200+70):27+6\right]:25\)

\(=\left[504-270:27+6\right]:25\)

\(=\left[504-10+6\right]:25\)

\(=\left[494+6\right]:25\)

\(=500:25=20\)

\(\text{Ko chắc }:)\)