Sin^2 a = 1-cos^2 a = 1-25/34=9/34
sin a = 3/√34
tga = sina/cosa = 3/√34 * (-√34/5) =-3/5
13.
a) При у= -1
cosx= -1
x=π+2πk, k∈Z
При к=2 x=π+2π*2=5π
б) При у=1/2
cosx=1/2
x₁=π/3 + 2πk, k∈Z
При к=2 x=π/3 + 2π*2 = π/3 + 4π = 13π/3
x₂= -π/3 + 2πk, k∈Z
При к=2 x= -π/3 + 2π*2= -π/3 + 4π = 11π/3
Ответ: 11π/3; 13π/3; 5π.
X²+x√10-25-(x²-25)=x²+x√10-25-x²+25=x√10
При х=√40 √40√10=√40*10=√400=20