X'2-12/5x-13=0
5x'2-12x-65=0
5x'2+13x-25x-65=0
x(5x+13)-5(5x+13)=0
(5x+13)(x-5)=0
5x+13=0 или x-5=0
x=-2,6 x=5
1)
7х+8=6х+1
7х-6х=1-8
х=-7
2)
5х+9=1
5х=1-9
5х=-8
х=-8:5
х=-1 3/5
3)
5х+4=х-12
5х-х=-12-4
4х=-16
х=-16:4
х=-4
1) 345+876=1221
2) 456*1221=556776
3) 254*678=172212
4) 172212-598=171614
5) 171614+556776=728390