\(\frac{91}{1.4}+\frac{91}{4.7}+\frac{9}{7.10}+...+\frac{91}{88.91}\)
= \(\frac{91}{3}\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{88.91}\right)\)
= \(\frac{91}{3}\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{88}-\frac{1}{91}\right)\)
= \(\frac{91}{3}.\frac{90}{91}=30\) (đfcm)
91/1.4+91/4.7+91/7.10+.....91/88.91 = 30
C1:Chứng minh : \(\frac{91}{1.4}+\frac{91}{4.7}+\frac{91}{7.10}+.....+\frac{91}{88.91}=30\)
C2:Cho n là số tự nhiên có 2 chữ số .Tìm n biết n+4 và 2n đều là các số chính phương
cmr 91/1.4+91/4.7+91/7.11+....+91/88.91
chứng minh :91/1*4+91/4*7+61/7*10+.......91/88*91=30
nếu đúng mình tick luôn
chứng minh rằng \(\frac{91}{1\cdot4}+\frac{91}{4\cdot7}+\frac{91}{7\cdot10}+......+\frac{91}{88\cdot91}\)=30
25 + ( x - 15 ) = 30
91 . 25 - 91 . 13 - 91 . 12
64 . 16 + 81. 84 + 17 . 16
2 câu cuối các bạn nào tính nhanh thì tihs giúp mik v ạ :>
Chứng minh rằng: 1 + 42 + 44 + ... + 42024 không chia hết cho 91
https://www.google.com/search?q=t%E1%BB%89+s%E1%BB%91+c%E1%BB%A7a+hai+s%E1%BB%91+l%C3%A0+3%2F4.+N%E1%BA%BFu+c%E1%BB%99ng+th%C3%AAm+60+v%C3%A0o+s%E1%BB%91+th%E1%BB%A9+nh%E1%BA%A5t+th%C3%AC+t%E1%BB%89+s%E1%BB%91+c%E1%BB%A7a+ch%C3%BAng+l%C3%A0+9%2F10.+T%C3%ACm+hai+s%E1%BB%91+%C4%91%C3%B3&oq=t%E1%BB%89+s%E1%BB%91+c%E1%BB%A7a+hai+s%E1%BB%91+l%C3%A0+3%2F4.+N%E1%BA%BFu+c%E1%BB%99ng++th%C3%AAm+60+v%C3%A0o+s%E1%BB%91+th%E1%BB%A9+nh%E1%BA%A5t+th%C3%AC+t%E1%BB%89+s%E1%BB%91+c%E1%BB%A7a+ch%C3%BAng+l%C3%A0+9%2F10.+T%C3%ACm+hai+s%E1%BB%91+%C4%91%C3%B3+++&aqs=chrome..69i57.118771j0j7&sourceid=chrome&ie=UTF-8#q=t%E1%BB%89+s%E1%BB%91+c%E1%BB%A7a+hai+s%E1%BB%91+l%C3%A0+3/4.+N%E1%BA%BFu+t%C4%83ng+th%C3%AAm+60+v%C3%A0o+s%E1%BB%91+th%E1%BB%A9+nh%E1%BA%A5t+th%C3%AC+t%E1%BB%89+s%E1%BB%91+c%E1%BB%A7a+ch%C3%BAng+l%C3%A0+9/10.+T%C3%ACm+hai+s%E1%BB%91+%C4%91%C3%B3
cho B=4/3+7/32+10/33+...+91/330
chứng minh rằng B<11/4
