Tìm x, biết : (a) 2(x+1)+3(x−5)=7.

a) \(2\left( {x + 1} \right) + 3\left( {x - 5} \right) = 7\)

\(2x + 2 + 3x - 15 = 7\)

\(5x - 13 = 7\)

5x = 20

x = 4.

Vậy x = 4.

b) \(\left( {x - 2} \right)\left( {x + 1} \right) - \left( {x + 5} \right)\left( {x - 3} \right) = 4\)

\(\left( {{x^2} - x - 2} \right) - \left( {{x^2} + 2x - 15} \right) = 4\)

\({x^2} - x - 2 - {x^2} - 2x + 15 = 4\)

−3x + 13 = 4

x = 3.

Vậy x = 3.