Знак минуса не увидели;
5х-15= -2х+8+6;
5х+2х=14+15;
7х=29;
х=29/7;
х=4 целых 1/7
Скорее так
<span>
2x-6>0 ; x>3</span>
B₁₀ = b₁ + 9d = 6,4 + 9*0,8 = 6,4 + 7,2 = 13, 6
Решение
<span>1. <span>Sin2xcosx+cos2xsinx=<span><span> </span></span></span></span>√3/2
<span><span><span><span>sin(2x + x) = </span></span></span></span>√3/2
<span><span><span><span>sin3x = </span></span></span></span>√3/2
<span><span><span><span>3x = (-1)^x arcsin(</span></span></span></span>√3/2) + πn, n∈ Z
<span><span><span><span>3x = (-1)^n *(</span></span></span></span>π/3) + πn, n∈Z
<span><span><span><span>x = (-1)^n *(</span></span></span></span>π/9) + πn/3, n∈Z
<span>2. <span>Cosx+cos</span></span>²<span><span>x=<span> 1/2 </span>- sin</span></span>²<span><span>x</span></span>
cosx = 1/2 - 1
cosx = - 1/2
x = (+ -)arccos(-1/2) + 2πn, n ∈ Z
x = (+ -)*(π - arccos(1/2)) + 2πn, n ∈ Z
x = (+ -)*(π - π/3) + 2πn, n∈Z
x = (+ -)*(2π/3) + 2πn, n∈Z
<span>3. <span>Sin3xcosx-cos3xsinx = </span></span>√3/2
<span><span>sin(3x - x) = </span></span>√3/2
<span><span>sin2x = </span></span>√3/2
<span><span>2x = (-1)^n arcsin(</span></span>√3/2) + πk, k ∈ Z
<span><span>2x = (-1)^n * (</span></span>π/3) + πk, k ∈ Z
x = (-1)^n * (π/6) + πk/2, k ∈ Z
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