2х+3х+40=90,
5х = 90-40,
5х = 50,
х = 10,
(4х+3)*(х-9)=0,
4х² - 36х + 3х - 27 = 0,
4х² - 33х - 27 = 0,
Д = (-33)² - 4*4*(-27) = 1089 + 432 = 1521,
х1 = (33 + 39) / 2*4 = 72 / 8 = 9,
х2 = (33 - 39) / 2*4 = -6 / 8 = -3/4 (или -0,75),
|х-5|=4,
х-5 = 4,
х = 4 + 5,
х1 = 9,
х-5 = -4,
х = -4+5,
х2 = 1