√72*cos²(15π/8)-3√2=3 , тк
1) По формуле
cos ²(α/2) = (1+cosα)/2 имеем
cos²(15π/8)=(cos²( (15π/4)/2 )= =
=(1+cos15π/4)/2=(1+√2/2)/2;
2) √72* (1+√2/2)/2 - 3√2=
=(√72+√144/2)/2 - 3√2=
=(6√2+6)/2 - 3√2=
=3√2+3 - 3√2=3
