\(=5+\dfrac{4}{5}\left(\dfrac{5}{2\cdot7}+\dfrac{5}{7\cdot12}+...+\dfrac{5}{52\cdot57}\right)\)
\(=5+\dfrac{4}{5}\left(\dfrac{1}{2}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{12}+...+\dfrac{1}{52}-\dfrac{1}{57}\right)\)
\(=5+\dfrac{4}{5}\cdot\dfrac{55}{114}=\dfrac{307}{57}\)
A= 2/ 2x7+ 2/ 7X+ 2/12x17+.........................+2/52X57
B= 5+ 4/2X7 +4/7X12+..................................+ 4/52X57
C= 2/3X9+ 2/9X15+......................................+2/57X63
3 tính nhanh tổng sau ; 5/2x7 + 5/7x12 + 5/17x12 + .... + 5/97x102
A=5/1x6+5/6x11+5/11x16+5/16x21+...+5/101x106
B=3/1x4+3/4x7+3/7x10+....+3/97x100
C=1/2x7+1/7x12+1/12x17+....+1/97x102
D=1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72
E=3/2x4+3/4x6+3/6x8+....+3/98x100
4/3x7+5/7x12+1/12x13+7/13x20+3/20x23=
Tính giá trị của biểu thức
20/2x7 + 20/7x12 + 20/12x17 + 20/17x22 + 20/22x27 + 20/27x32
Tìm X biết 4/3x7 + 5/7x12 + 1/12x13 + 7/13x20 + 3/20x23 + 5/Xx(X-5) = 11/18
4/3x7 + 5/7x12 + 1/12x13 + 7/13x20 + 3/20x23
Giải ra cho mình nhé
Ai giúp mình với nghĩ mãi ko ra :
4/3x7 + 5/7x12 + 1/12x13 + 1/20x23
\(\frac{4}{3x7}+\frac{5}{7x12}+\frac{1}{12x13}+\frac{7}{13x20}+\frac{3}{20x23}\)
