Find the value of y such that $$\tan(y°)=(4\cos^29°-3)(4\cos^227°-3)$$
I let $x = 9°$ And equation become $$(2\cos2x-1)(2\cos6x-1)$$
Then I tried to convert cos in tan using half angle formula but it didn't work .
I also found $\cos(4x+6x)=0 \implies \tan4x\tan6x=1$ But I failed to convert in a form from where I can calculate y.
Thanks in advance for any help