Cho phản ứng xFeS2 + yH2SO4 (đặc, nóng) -> zFe(SO4)3 + tSO2 + aH2O. Các giá trị a ; x ; y ; t ; z lần lượt là:
A. 2 ; 14 ; 15 ; 1 ; 14

B. 1 ; 14 ; 14 ; 15 ; 2

C. 15 ; 2 ; 14 ; 14 ; 1

D. 14 ; 2 ; 14 ; 15 ; 1

Tính nhẩm rồi điền kết quả vào chỗ trống.

14 - 1 = 13     15 - 4 = 11     17 - 2 = 15     15 - 3 = 12

15 - 1 = 14     19 - 8 = 11     16 - 2 = 14     15 - 2 = 13

a,=\(\dfrac{8}{14}-\dfrac{1}{14}+\dfrac{5}{21}+\dfrac{3}{2}\)

=\(\dfrac{1}{2}+\dfrac{3}{2}+\dfrac{5}{21}\) =\(2+\dfrac{5}{21}\) =\(\dfrac{42}{21}+\dfrac{5}{21}\) =\(\dfrac{47}{21}\)

b,=\(\dfrac{11}{13}.\dfrac{12}{15}-\dfrac{7}{15}+\dfrac{14}{15}.\dfrac{11}{13}\)

=\(\dfrac{11}{13}.\left(\dfrac{12}{15}+\dfrac{14}{15}\right)-\dfrac{7}{15}\)

=\(\dfrac{11}{13}.\dfrac{26}{15}-\dfrac{17}{15}\) =\(\dfrac{22}{15}-\dfrac{17}{15}\) =\(\dfrac{5}{15}\) =\(\dfrac{1}{3}\)

c,=\(\left(\dfrac{3}{6}-\dfrac{2}{6}\right)^2\) =\(\left(\dfrac{1}{6}\right)^2\) =\(\dfrac{1}{36}\)

d,=câu này dễ mà

a) x + 3/5 = -1/15

=> x = -1/15 - 3/5

=> x = -2/3

b) x/14 = 1/7 - 3/14

=> x/14 = -1/14

=> x = -1

c) -1/2x + 1/5 = 3/10

=> -1/2x = 3/10 - 1/5

=> -1/2x = 1/5

=> x = 1/5 : (-1/2)

=> x = -2/5

d) 4/5 - (2/15 + x) = 1/15

=> 4/5 - 2/15 - x = 1/15

=> 2/3 - x = 1/15

=> x = 2/3 - 1/15

=> x = 3/5

a) 8/15 + 1 = 23/15

b) 3/14 + 11/14 - 2/3 = 1- 2/3 = 1/3

c) 7/15 * (5/3+2/3) = 7/15 * 7/3= 49/45

d) 6/11 + 5/11 - 3/5 = 1 - 3/5 = 2/5

a=23/18

b=1/3

c=49/4

d=2/5

\(\dfrac{1}{15};\dfrac{2}{15};\dfrac{11}{15};\dfrac{14}{15};1;2;\dfrac{16}{5};5;\dfrac{26}{3};\dfrac{390}{13}\)

`@` `\text {Ans}`

`\downarrow`

`M = (-15)+(-14)+(-13)+(-12)+...+14+15`

`= (-15+15) + (-14+14) + (-13+13) + ... (-1 + 1) + 0`

`= 0`