5cos2α = 5(cos²α - sin²α) = 5(1 - sin²α - sin²α) = 5(1 - 2sin²α) =
= 5(1 - 2· (-0,4)²) = 5(1 - 0,32) = 5 · 0,68 = 3,4
log6(16)=log6(2^4)=4log6(2)=4/log2(3*2)= log12(2)=a log2(12)=1/a
=4/(log2(3)+log2(2))=4/(log2(3)+1) log2(3*4)=1/a log2(3)+log2(4)=1
log6(16)=4/(1/a-2+1)=4a/(1-a) log2(3)+2=1/a log2(3)=1/a-2