tính nhanh: 2/5*7+2/7*9+2/9811+...+2/13*15
tính nhanh 2/3*5+2/5*7+/7*9+....2/13*15
\(\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+...+\frac{2}{13\cdot15}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{13}-\frac{1}{15}\)
\(=\frac{1}{3}-\frac{1}{15}\)
\(=\frac{4}{15}\)
\(\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{13\cdot15}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{13}-\frac{1}{13}+\frac{1}{15}-\frac{1}{15}\)
\(=\frac{1}{3}-\frac{1}{15}=\frac{4}{15}\)
\(\frac{2}{3.5}\)+ \(\frac{2}{5.7}\)+ \(\frac{2}{7.9}\)+...+ \(\frac{2}{13.15}\)= \(\frac{1}{3}\)- \(\frac{1}{5}\)+ \(\frac{1}{5}\)- \(\frac{1}{7}\)+ \(\frac{1}{7}\)- \(\frac{1}{9}\)+...+ \(\frac{1}{13}\)- \(\frac{1}{15}\)= \(\frac{1}{3}\)- \(\frac{1}{15}\)= \(\frac{4}{15}\).
Tính nhanh:
a. -3/7+15/26-(2/13-3/7)
b.2*3/7+(2/9-10/7)-5/3: 1/9
tính nhanh A=1/3-3/4-(-3/5)+1/72-2/9-1/36+1/15
B=1/5-3/7+5/9-2/11+7/13-9/6-7/13+2/11-5/9-3/7-1/5
C1/100-1/100.99-1/99.98-1/98.87-...-1/3.2-1/2.1
Bài 1 Tính nhanh
a) -3/7 + 5/13 + 3/7
b) -5/21+-2/21+8/24
c) -5/11+(-6/11+2)
d) (-1/32+1/2)+15/32
e)5/17+ -6/13 + 3/4 + 7/-13+12/17
f) 7/23+-18/18+-4/9+16/23+-5/8
g)1/3+-3/4+3/5+-1/36+1/15+-2/9
h)-1/2+1/3+-1/4+-2/8+4/18+4/9
a)\(-\dfrac{3}{7}+\dfrac{5}{13}+\dfrac{3}{7}\)
=\(\left(-\dfrac{3}{7}+\dfrac{3}{7}\right)+\dfrac{5}{13}\)
=\(0+\dfrac{5}{13}\)
=\(\dfrac{5}{13}\)
Bài 1:Tính nhanh: a, 2/3 x4/9+2/3x5/9 b,5/9x4/7+13/9x7/4
c, 32/16x3/2-1/2x32/19 d,15/16x 9/5-15/16x4/5 e,13/25x5-13/25x3-13/25]
bạn nào học giỏi giúp mình với?
a: =2/3(4/9+5/9)=2/3
d: =15/16(9/5-4/5)=15/16
e: =13/25(5-3-1)=13/25
tính nhanh :
A = 1/3 - 3/4 -(-3/5) +1/72-2/9-1/36+1/15
B= 1/5 -3/7 +5/9 -2/11+7/13-9/16-7/13+2/11-5/9+3/7 -1/5
C= 1/100-1/100.99- 1/99.98-1/98.97......-1/3.2 - 1.2.1
E=-6/7+6/13-6/29 trên 9/7-9/13+9/29
F=2/15-2/21+2/29 trên 0.25 - 5/28+5/52
đề bài là tính nhanh nhé
c.ơn các bạn
\(E=\frac{\frac{-6}{7}+\frac{6}{13}-\frac{6}{29}}{\frac{9}{7}-\frac{9}{13}+\frac{9}{29}}=\frac{-6.\left(\frac{1}{7}-\frac{1}{13}+\frac{1}{29}\right)}{9.\left(\frac{1}{7}-\frac{1}{13}+\frac{1}{29}\right)}=\frac{-6}{9}=\frac{-2}{3}\)
\(F=\frac{\frac{2}{15}-\frac{2}{21}+\frac{2}{39}}{0,25-\frac{5}{28}+\frac{5}{52}}=\frac{\frac{2}{3}.\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{13}\right)}{\frac{1}{4}-\frac{5}{28}+\frac{5}{52}}\)
\(=\frac{\frac{2}{3}.\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{13}\right)}{\frac{5}{4}.\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{13}\right)}=\frac{2}{3}:\frac{5}{4}=\frac{2}{3}.\frac{4}{5}=\frac{8}{15}\)
Bạn soyeon ơi! Hình như câu đầu bạn làm sai rồi thì phải. Họ ra đề là + đến - nhưng bạn làm - đến +.
BÀI 1 : TÍNH NHANH
A) (1/9 - 9/17 ) + 3/6 - (12/17 - 1/2 ) + 5/9
B) 7/32 × ( -9/12 - 16/30 ) - ( 7/32 - 15 )
C) 3/10 × ( -5/9 + 3/5 ) - 3/10 × ( 3/9 + -2/5 )
D) -2/5 × ( 5/17 - 9/15 ) - 2/5 × ( 2/17 + -2/5 )
E) [ -5/13 - ( 3/5 +3/13 - 4/10 ) ] ÷ -15/11
G) 2/19 × ( -9/27 × 54/63 ÷ 5/7 )
\(\dfrac{-1}{9}.\dfrac{-3}{5}+\dfrac{5}{-6}.\dfrac{-3}{5}-\dfrac{7}{2}.\dfrac{3}{5}\)
\(\dfrac{-3}{7}.\dfrac{15}{13}.\dfrac{3}{7}.\dfrac{11}{13}-\dfrac{3}{7}\)
Đề bài: Tính nhanh