Решение
<span>1) a</span>₅ <span>= a</span>₁₇ <span>- 12d
</span><span>86 = 104 - 12d
</span><span>12d = 18
</span><span>d = 1,5
</span><span>2) an=a</span>₁ <span>+ (n - 1)d
</span><span>a</span>₅ <span>= a</span>₁ <span>+ 4d
</span><span>86 = a</span>₁ <span>+ 4*1,5
</span><span>a</span>₁<span>=80</span>
<span>1) 2cosx/2=1, Cosx/2 = 1/2, ⇒ х/2 = +-π/3 +2πk, k ∈Z х = +-2π/3 + 4πk, k ∈ Z2) 3tgx-√3=0, tgx = √3/3 x = π/6 + πk , k ∈ Z3) Cos(3p/2+x) -1=0, Sinx = 1 x = π/2 + 2πk , k ∈ Z 4) 2Ctg²X=1/Sin²X -1. 2Cos²x = 1 - Sin²x 2Cos²x = 1 - 1 + Cos²x Cos²x = 0 Cosx = 0 x = π/2 + πk , k∈Z5) вычислить наибольший отрицательный корень: Sin π/2 tg(-x)= - √3/3 - tgx = - √3/3 tgx = √3/3 x = π/6 + πk , k ∈ ZОтвет: х = -5π/6</span>