Это дискриминант решение нижи
Х+6=5+4х
х-4х=5-6
-3х=-1
х=-1/(-3)
х=1/3
13-3(х+1)=4-5х
13-3х-3=4-5х
-3х+5х=4-13+3
2х=-8
х=-8/2
х=-4
<span>
0,2(3х-5)-0,3(х-14)=-0,7
</span>0.6х-1-0.3х+4.2=-0.7
0.3х=-0.7+1-4.2
0.3х=-3.9
х=-3.9/0.3
х=-13
<span>
-6=-2-(4+9х)</span>
-6=-2-4-9х
-9х=-2-4+6
-9х=0
х=-9
<span>1,2(5-4х)=-6(0,8х+1)
</span>6-4.8х=-4.8х-6
-4.8х+4.8х=-6-6
х=-12
Cos(2*15°) =<span>cos(30°) =</span> ½√3