toan HACK NAO
100+2=200
316+2=732
103-2+2=103
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(101+102+...+200)+(-1-2-3-...-100)
=(101-1)+(102-2)+...+(200-100)
=100+100+...+100
=100*100=10000
\(\text{1+2+3+4+5+...+100-101-102-103-...-200}\)
\(\text{=1+2+3+4+5+...+100-(100+1)-(100+2)-(100+3)-...-(100+100)}\)
\(\text{=1+2+3+4+5+...+100-100-1-100-2-100-3-...-100-100}\)
\(\text{=(1+2+3+4+5+...+100-1-2-3-...-100)-100-100-100-...-100}\)(có 100 số 100)
\(=0-100-100-100-...-100\)(có 100 số 100)
\(=-10000\)
a, =25- 62-25 +12
= (25-25)+12-62
= -50
b, = -24 -68+24 + 2. (-60)
= (-24+24)-68 + -120
= -188
c,
Ta có:\(\dfrac{1}{101}+\dfrac{1}{102}+...+\dfrac{1}{200}>\dfrac{1}{200}+\dfrac{1}{200}+...+\dfrac{1}{200}=\dfrac{100}{200}=\dfrac{1}{2}\)
Lại có:
\(\dfrac{1}{101}+\dfrac{1}{102}+...+\dfrac{1}{200}< \dfrac{1}{101}+\dfrac{1}{101}+...+\dfrac{1}{101}=\dfrac{100}{101}\)
Vậy ...
Những dãy trên đều có 100 số hạng.
\(\frac{3}{7.10}+\frac{3}{10.13}+....+\frac{3}{100.103}\)
\(=\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+....+\frac{1}{100}-\frac{1}{103}\)
\(=\frac{1}{7}-\frac{1}{103}\)
\(=\frac{96}{721}\)
\(\frac{2}{7.10}+\frac{2}{10.13}+...+\frac{2}{100.103}\)
\(=\frac{2}{3}\left(\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{100}-\frac{1}{103}\right)\)
\(=\frac{2}{3}\left(\frac{1}{7}-\frac{1}{103}\right)\)
\(=\frac{2}{3}.\frac{96}{721}\)
\(=\frac{64}{721}\)
\(A=\)\(\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{100.103}\)
\(A=\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{100}-\frac{1}{103}\)
\(A=\frac{1}{7}-\frac{1}{103}\)
\(A=\frac{96}{721}\)
\(B=\frac{2}{7.10}+\frac{2}{10.13}+...+\frac{2}{100.103}\)
\(B=2\left(\frac{1}{7.10}+\frac{1}{10.13}+...+\frac{1}{100.103}\right)\)
\(3B=2.3\left(\frac{1}{7.10}+\frac{1}{10.13}+...+\frac{1}{100.103}\right)\)
\(3B=2\left(\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{100.103}\right)\)
\(3B=2\left(\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{100}-\frac{1}{103}\right)\)
\(3B=2\left(\frac{1}{7}-\frac{1}{103}\right)\)
\(3B=2.\frac{96}{721}\)
\(3B=\frac{192}{721}\)
\(\Rightarrow B=\frac{192}{721}:3\)
\(B=\frac{64}{721}\)
\(A=\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{100.103}\)
\(A=\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{100}-\frac{1}{103}\)
\(A=\frac{1}{7}-\frac{1}{103}\)
\(A=\frac{96}{721}\)
Vậy \(A=\frac{96}{721}\)
\(B=\frac{2}{7.10}+\frac{2}{10.13}+...+\frac{2}{100.103}\)
\(B=\frac{2}{3}.\left(\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{100.103}\right)\)
\(B=\frac{2}{3}.\left(\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{100}-\frac{1}{103}\right)\)
\(B=\frac{2}{3}.\left(\frac{1}{7}-\frac{1}{103}\right)\)
\(B=\frac{2}{3}.\frac{96}{721}\)
\(B=\frac{64}{721}\)
Vậy \(B=\frac{64}{721}\)
_Chúc bạn học tốt_
Ta có :
\(1.3.5.7.....199\)
\(=\frac{1.2.3.4.5.6.7.....198.199.200}{2.4.6.....198.200}\)
\(=\frac{\left(1.2.3.....99.100\right)\left(101.102.....200\right)}{\left(1.2.3.....99.100\right)\left(2.2.2.....2.2\right)}\)
\(=\frac{101.102.....200}{2.2.....2}\)
\(=\frac{101}{2}.\frac{102}{2}.....\frac{200}{2}\left(đpcm\right)\)
EZ TRẢ LỜI XONG NHỚ T.I.C.K
100X2=200
316X2=632(CHỨ KO PHẢI 732)
103:2X2=103
HT
100 + 2 = 102 ( chứ ko phải là 200 nha )
316 + 2 = 318 ( chứ ko phải là 732 nha )
còn PT số 3 đg òi nha