Tìm x biết 1. (19 − 51) − (x − 23) = 6; 2. −5x − 10 · (−7) = 55

* Hướng dẫn giải

1. (19 − 51) − (x − 23) = 6

19 − 51 − x + 23 = 6

−x = 6 − 19 + 51 − 23

−x = 15

x = −15.

2. −5x − 10.(−7) = 55

−5x + 70 = 55

−5x = 55 − 70

−5x = −15

x = (−15) : (−5)

x = 3.