D=1.2+3.4+6.8+...+200+202
D=\(\dfrac{1.2+2.4+3.6+4.8+5.10}{3.4+6.8+9.12+12.16+15.20}\)
Ta có:
\(D=\dfrac{1.2+2.4+3.6+4.8+5.10}{3.4+6.8+9.12+12.16+15.20}\\ =\dfrac{1.2+1.2.4+1.2.3.3+1.2.2.8+1.2.5.5}{3.4+3.4.2.2+3.4.3.3+3.4.2.8+3.4.5.5}\\ =\dfrac{1.2\left(4+3^2+2.8+5^2\right)}{3.4\left(2^2+3^2+2.8+5^2\right)}\\ =\dfrac{1.2}{3.4}=\dfrac{1}{6}\)
Vậy \(D=\dfrac{1}{6}\)
2.4+4.6+6.8+...+98.100/1.2+2.3+3.4+...+49.50. Tính
\(\frac{2.4+4.6+6.8+...+98.100}{1.2+2.3+3.4+...+49.50}=\frac{4.\left(1.2+2.3+3.4+...+49.50\right)}{1.2+2.3+3.4+...+49.50}=\frac{4}{1}=4\)
\(\text{Tính: }\dfrac{1.2+2.4+3.6+4.8+5.10}{3.4+6.8+9.12+12.16+15.20}\)
\(\dfrac{1.2+2.4+3.6+4.8+5.10}{3.4+6.8+9.12+12.16+15.20}\)
\(=\dfrac{1.2+2.4+3.6+4.8+5.10}{3.4+3.4.2.2+3.4.3.3+3.4.2.8+3.4.5.5}\)
\(=\dfrac{1.2.\left(4+3^2+2.8+5^2\right)}{3.4.\left(4+3^2+2.8+5^2\right)}\)
\(=\dfrac{1}{6}\)
\(\dfrac{1.2+2.4+3.6+4.8+5.10}{3.4+6.8+9.12+12.16+15.20}\)
\(=\dfrac{1.2+1.2.2^2+1.2.3^2+1.2.4^2+1.2.5^2}{3.4+3.4.2^2+3.4.3^2+3.4.4^2+3.4.5^2}\)
\(=\dfrac{1.2\left(1+2^2+3^2+4^2+5^2\right)}{3.4\left(1+2^2+3^2+4^2+5^2\right)}\\ =\dfrac{2}{12}=\dfrac{1}{6}\)
\(\dfrac{1.2+2.4+3.6+4.8+5.10}{3.4+6.8+9.12+12.16+15.20}\)
= \(\dfrac{2\left(1+4+9+16+25\right)}{4\left(3+12+27+48+65\right)}\)
= \(\dfrac{2.55}{4.155}\)
= \(\dfrac{1.55}{2.155}\)
= \(\dfrac{55}{310}=\dfrac{11}{62}\)
A=1.2+2.3+3.4+.....+79.80
B=2.4+4.6+6.8+....+48.50
gọi tổng của 1+2+3+4+...+79 là M
2+3+4+...+80 là N
ta có A = M.N
từ 1 đến 79 hay từ 2 đến 80 có (79-1) chia 1 + 1=79
M = (79+1).79 chia 2= 3160
N = (80+2).79chia 2= 3239
A = 3160 .3239 = 10235240
1.2+2.4+3.6+4.8+5.10/3.4+6.8+9.12+12.16+15.20
Tính nhanh biểu thức: 1.2+2.4+3.6+4.8+5.10/3.4+6.8+9.12+12.16+15.20
Tính nhanh
1.2+2.4+3.6+4.8+5.10
--------------------------------------
3.4+6.8+9.12+12.16+15.20
\(\frac{1.2+2.4+3.6+4.8+5.10}{3.4+6.8+9.12+12.16+15.20}\)
So sánh A và B biết : A = 1.2+2.4+3.6+4.8+5.10/3.4+6.8+9.12+12.16+15.20 va B = 111111/666665
tính L=\(\frac{1.2+2.4+3.6+4.8+5.10}{3.4+6.8+9.12+12.16+2.10}\)