a) A = \(\dfrac{2000.2001-1000}{2000.2000+1000}=\dfrac{2000.2000+2000-1000}{2000.2000+1000}=1\)
b) \(\left(y+1\right)+\left(y+2\right)+\left(y+3\right)+...+\left(y+50\right)=1425\)
<=> \(50y+\left(50+1\right).\left[\left(50-1\right):1+1\right]:2=1425\)
<=> \(50y+1275=1425\)
<=> \(50y=150\) <=> y = 3
a) A=\(\dfrac{2000.2001-1000}{2000.2000+1000}\)
A=\(\dfrac{2000.\left(2000+1\right)-1000}{2000.2000+1000}\)
A=\(\dfrac{2000.2000+2000-1000}{2000.2000+1000}\)
A=\(\dfrac{2000-1000}{1000}\)
A=\(\dfrac{1000}{1000}\)=1
\(b\)) \(\left(y+1\right)+\left(y+2\right)+\left(y+3\right)+......+\left(y+50\right)=1425\)
\(< =>50y+\left(1+49\right)+\left(2+48\right)+.....+\left(24+26\right)+25+50=1425\)
\(< =>50y+24\left(1+49\right)+75=1425\)
\(< =>50y+1275=1425\)
\(< =>50y=150\)
\(=>y=3\)
b) Từ dãy số trên suy ra có 50 số y
Tổng các số từ 1 đến 50 là: (50+1).50:2=1275
y.50+1275=1425
y.50 =1425-1275=150
y = 150:50=30
Vậy y=30
Giải:
a) \(A=\dfrac{2000.2001-1000}{2000.2000+1000}\)
\(A=\dfrac{2000.\left(2000+1\right)-1000}{2000.2000+1000}\)
\(A=\dfrac{2000.2000+2000-1000}{2000.2000+1000}\)
\(A=\dfrac{2000.2000+1000}{2000.2000+1000}\)
\(A=1\)
b) \(\left(y+1\right)+\left(y+2\right)+\left(y+3\right)+...+\left(y+50\right)=1425\)
\(\Rightarrow50.y+\left(1+2+3+...+50\right)=1425\)
Số số hạng của dãy (1+2+3+...+50):
(50-1):1+1=50
Tổng dãy (1+2+3+...+50):
(1+50).50:2=1275
\(\Rightarrow50.y+1275=1425\)
\(50.y=1425-1275\)
\(50.y=150\)
\(y=150:50\)
\(y=3\)
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