dãy số trên có 2 số hạng liền nhau hơn kém nhau 2 đơn vị 

dãy  số trên có số số hạng là :

( 212-2 ) : 2 +1= 106 ( số )

tổng dãy số trên là :

( 212 +2) * 106 : 2 = 11342 

đáp số : 11342

Số số hạng là:
        (212-2):2+1=106 (số)
Tổng là:
        (2+212).106:2=11342
           Đáp số :11342

Số số hạng : 

( 212 - 2 ) / 2 + 1 = 106 

Tổng : 

( 212 + 2 ) x 106 / 2 = 11342 

a) \(212+109+188\)

\(=\left(212+188\right)+109\)

\(=400+109\)

\(=509\)

b) \(27+45+18+81\)

\(=72+99\)

\(=171\)

c) \(\left(14+72+36+60\right):12\)

\(=182:12\)

\(=\frac{91}{6}\)

bạn ơi mình lớp 6 cơ tính  bằng cach hợp lí phần c) không đc đổi ra phân số bạn ạ lớp 6 mà

a) 212 + 109 + 188

= ( 212 + 188 ) + 109

= 400 + 109

= 509

b) 27 + 45 + 18 + 81

= ( 27 + 18 ) + 45 + 81

= 45 + 45 + 81

= 90 + 81

= 171

c) ( 14 + 72 + 36 + 60 ) : 12

= ( 14 + 36 ) : 12 + ( 72 + 60 ) : 12

= 50 : 12 + 132 : 12

= ( 132 + 50 ) : 12

= 182 : 12

= 15,1666

-159+(-19)+59+(-81)

=-159+59-19-81

=100-19-81

=100-(19+81)

=100-100

=0

-135-(-112)-(-135)+212

=-135+112+135+212

=-23+135+212

=112+212

=324

a)(-159)+(-19)+59+(-81)

=(-159)+59+(-19)+(-81)

=(-100)+(-100)

=(-200)

b)(-135)-(-112)-(-135)+212

=(-135)+112+135+212

=(-135)+135+112+212

=324

Chúc bn học tốt

(-159)+(-19)+59+(-81)=(-159+59)+(-19+(-81))=(-100)+(-100)+=-200

(-135)-(-112)-(-135)+212=(-135-(-135))-(-112+212)=0-100=-100

Mình là lính mới nên có gì sai thì xin lỗi tha!

1. \(PTK_{Fe_2\left(SO_4\right)_x}=56.2+\left(32+16.4\right).x=400\left(đvC\right)\)

=> x = 3

2. \(PTK_{K_3\left(PO_4\right)_y}=39.3+\left(31+16.4\right).y=212\left(đvC\right)\)

=> y = 1

a) -3 b) -57  c) 12 d) -100

\(\left(-2021\right).\left(23+76\right)-2021=\left(-2021\right).99-2021=-202100\)

=-2021x100=-202100

\(5,-\dfrac{2}{7}-\left(\dfrac{5}{11}-\dfrac{9}{7}\right)+\dfrac{5}{11}=-\dfrac{2}{7}-\dfrac{5}{11}+\dfrac{9}{7}+\dfrac{5}{11}=\left(-\dfrac{2}{7}+\dfrac{9}{7}\right)-\left(\dfrac{5}{11}-\dfrac{5}{11}\right)=1-0=1\\ 6,\dfrac{2}{3}+\dfrac{-2}{5}+\dfrac{-5}{6}-\dfrac{13}{10}=\left(\dfrac{4}{6}+\dfrac{-5}{6}\right)+\left(\dfrac{-4}{10}-\dfrac{13}{10}\right)=\dfrac{-1}{6}+\dfrac{-17}{10}=\dfrac{-5}{30}+\dfrac{-51}{30}=\dfrac{-56}{30}=\dfrac{-28}{15}\)

\(7,\dfrac{-5}{9}+\dfrac{8}{15}+\dfrac{4}{-9}+\dfrac{7}{15}=\left(\dfrac{-5}{9}+\dfrac{-4}{9}\right)+\left(\dfrac{8}{15}+\dfrac{7}{15}\right)=\left(-1\right)+1=0\\ 8,\left(\dfrac{12}{13}+7\right)-\left(-\dfrac{1}{13}+8\right)=\dfrac{12}{13}+7+\dfrac{1}{13}-8=\left(\dfrac{12}{13}+\dfrac{1}{13}\right)+\left(7-8\right)=1+\left(-1\right)=0\)

a) \(\left(\dfrac{3}{8}-\dfrac{1}{5}-\dfrac{1}{3}\right)+\left(\dfrac{5}{8}-1\dfrac{3}{7}-\dfrac{4}{7}\right)+\dfrac{1}{3}\)

\(=\dfrac{3}{8}-\dfrac{1}{5}-\dfrac{1}{3}+\dfrac{5}{8}-\dfrac{10}{7}-\dfrac{4}{7}+\dfrac{1}{3}\)

\(=\left(\dfrac{3}{8}+\dfrac{5}{8}\right)+\left(\dfrac{-1}{3}+\dfrac{1}{3}\right)+\left(\dfrac{-10}{7}-\dfrac{4}{7}\right)-\dfrac{1}{5}\)

\(=1+0+\left(-2\right)-\dfrac{1}{5}\)

\(=-1-\dfrac{1}{5}\)

\(=\dfrac{-6}{5}\)

b) \(-24.\left(\dfrac{1}{3}-\dfrac{1}{4}\right)^2-1,5\)

\(=-24.\left(\dfrac{1}{12}\right)^2-\dfrac{3}{2}\)

\(=-24.\dfrac{1}{144}-\dfrac{3}{2}\)

\(=\dfrac{-1}{6}-\dfrac{3}{2}=\dfrac{-1}{6}-\dfrac{9}{6}=\dfrac{-10}{6}=\dfrac{-5}{3}\)

c) \(2^2-\left(-\dfrac{5}{7}\right)^0+\left(\dfrac{1}{3}\right)^4.3^6\)

\(=4-1+\dfrac{1}{81}.729\)

\(=4-1+9\)

\(=3+9=12\)

d) \(23\dfrac{1}{3}:\left(\dfrac{-5}{7}\right)+13\dfrac{1}{3}:\dfrac{5}{7}\)

\(=\dfrac{-70}{3}.\dfrac{7}{5}+\dfrac{40}{3}.\dfrac{7}{5}\)

\(=\dfrac{7}{5}\left(\dfrac{-70}{3}-\dfrac{40}{3}\right)\)

\(=\dfrac{7}{5}.\left(-10\right)\)

\(=-14\)

e) \(\dfrac{3}{4}.\dfrac{8}{5}+\dfrac{6}{15}:\dfrac{4}{3}-1\dfrac{2}{5}:1\dfrac{1}{3}\)

\(=\dfrac{3}{4}.\dfrac{8}{5}+\dfrac{6}{15}.\dfrac{3}{4}-\dfrac{7}{5}.\dfrac{3}{4}\)

\(=\dfrac{3}{4}\left(\dfrac{8}{5}+\dfrac{6}{15}-\dfrac{7}{5}\right)\)

\(=\dfrac{3}{4}\left(\dfrac{24}{15}+\dfrac{6}{15}-\dfrac{21}{15}\right)\)

\(=\dfrac{3}{4}.\dfrac{9}{15}\)

\(=\dfrac{9}{20}\)

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