Question

C = 6/15.18 + 6/18.21 +..........+6/87.90

Giups mk nha mk đg cần gấp

Answer 1

C = 6 / 15.18 + 6 / 18.21 + .......... + 6 / 87.90

3c= 3/15.18 + 3/18.21+...........+3/87.90

    =1/15 - 1/18 + 1/18 -1/21 +.............+1/87-1/90

    =1/15-1/90

    =75/1350

C=75/1350 X 2 

C=75/675                                          NHỚ TK CHO MÌNH NHA BẠN !

Answer 2

C=6 x \(\frac{1}{3}\left(\frac{1}{15}-\frac{1}{18}+\frac{1}{18}-\frac{1}{21}+.....+\frac{1}{87}-\frac{1}{90}\right)\)

C= 6 x \(\frac{1}{3}\left(\frac{1}{15}-\frac{1}{90}\right)\)

C= 6 x \(\frac{1}{3}x\frac{1}{18}\)

C =1/9

Answer 3

=6x(1/15x18+1/18x21+....1/87x90)

=6x1/15+1/90

=2/5+1/90

=37/90