Cos (5π/2 + α) = - 0.6 α - в 1-й четверти
Cos (5π/2 + α) = сos (π/2 + α) = -sin α = -0.6
sin α = 0.6
cos α = √1 - 0.36 = 0.8
Cos (5π + α) = cos (π + α) = - cos α = -0.8
Ответ: cos (5π + α) = -0.8
А=sin90*tg45+2cos180 = 1*1+2*-1=-1
B=cosп/2*ctgп/3+4sin п/6 =0*√3/3+4*1/2=2
a*b=-1*2=-2
<span>(2.5у-4)(6у+1.8)=0</span>
Решение
sin3x - cos5x = 0
cos(π/2 - 3x) - cos5x = 0
- 2cos(π/2 - 3x + 5x)/2 * sin(π/2 - 3x - 5x)/2 = 0
1) cos(π/4 + x) = 0
π/4 + x = π/2 + πk, k ∈ Z
x = π/2 - π/4 <span>+ πk, k ∈ Z
x = </span>π/4 <span>+ πk, k ∈ Z
2) sin(</span>π/4 - 4x) = 0
4x - π/4 = πn, n ∈ Z
<span>4x = π/4 + πn, n ∈ Z
</span>x = π/16 + πn/4, n ∈ Z
x = π/16 - <span>наименьшее положительное решение </span>