cos2x-10cosx-11=0
2cos^2x-1-10cosx-11=0
2cos^2x-10cosx-12=0
cos^2x-5cosx-6=0
x2 - 5x - 6 = 0
D = b2 - 4ac
D = 25 + 24 = 49 = 7^2
x1,2 = -b ± √D/2a
x1 = 5 + 7/2 = 12/2= 6
x2 = 5 - 7/2 = - 2/2 = -1
x1 = 6; x2 = -1
cosx=6 - (не удолт)
cosx=-1 -> x=pi+2pi*k , к-N
8,4x+3-5(7,2x+0,3)=8,4x+3-36x-1,5=-27,6x-1.5
³√25*<span>³√135=</span>³√5^2*5*27=<span><span>³√</span>5^3*3^3=5*3=15</span>