<u />15ху+3у- 5х-1 = 5х(3у<u /><u />-1) - 1(3у-1) = (3у-1) (5х-1)
Cos^2(3x) - sin^2(3x) - cos 4x = 0
cos(2*3x) - cos4x = 0
cos6x - cos4x = 0
(- 2sin((6x+4x)/2))*(sin((6x-4x)/2)) = 0
-2sin5x*sinx = 0
разделим на -2
sin5x = 0
5x = πn, n ∈ z
x = πn/5, n ∈ z
sinx = 0
x = πn, n ∈ z
SinA=BC/AC=2,8/5,6=1/2
<A=30
<B=90-<A=90-30=60