So sánh A và B : \(A=\dfrac{20^{10}+1}{20^{10}-1}\) và \(B=\dfrac{20^{10}-1}{20^{10}-3}\)

Tính:

a) \(\dfrac{-5}{6}+\dfrac{1}{6}\)

b) \(\dfrac{1}{3}-\dfrac{5}{4}.\dfrac{4}{15}\)

c) \(4.\left(-5\right)^2+\left(-2\right)^3.25\)

d) \(\dfrac{-2}{7}+\dfrac{1}{5}:\dfrac{7}{15}\)

Tìm x:

a) \(x\) + \(\dfrac{-3}{7}=\dfrac{4}{7}\).

b) \(\dfrac{1}{2}x-75\%=\dfrac{1}{4}.\)

c) \(\left|x-\dfrac{2}{3}\right|+2,25=\dfrac{3}{4}\).

12 + ( x - 15 ) = 0

x - 15 = 0 - 12

x - 15 = -12

x = ( - 12 ) + 15

x = 3.

Vậy x = 3.

12 + ( x - 4 ) = 0

( x - 4 ) = 0 - 12

x - 4 = -12

x = ( - 12 ) + 4

x = -8.

Vậy x = -8.