To prove the inequality sinπ/3−2xπ/3 - 2xπ/3−2xcosπ/3−2xπ/3 - 2xπ/3−2x ≥ -√3/4, we can use the double angle formula for sine and cosine:
sin2θ2θ2θ = 2sinθθθcosθθθ cos2θ2θ2θ = cos^2θθθ - sin^2θθθ
Let's first substitute θ = π/6 - x into the double angle formulas:
sinπ/3−2xπ/3 - 2xπ/3−2x = 2sinπ/6−xπ/6 - xπ/6−xcosπ/6−xπ/6 - xπ/6−x cosπ/3−2xπ/3 - 2xπ/3−2x = cos^2π/6−xπ/6 - xπ/6−x - sin^2π/6−xπ/6 - xπ/6−x
Now, substitute these expressions back into the original inequality:
2sinπ/6−xπ/6 - xπ/6−xcosπ/6−xπ/6 - xπ/6−xcos2(π/6−x)−sin2(π/6−x)cos^2(π/6 - x) - sin^2(π/6 - x)cos2(π/6−x)−sin2(π/6−x) ≥ -√3/4
Expand the expression and simplify:
2sinπ/6−xπ/6 - xπ/6−xcosπ/6−xπ/6 - xπ/6−xcos^2π/6−xπ/6 - xπ/6−x - 2sin^3π/6−xπ/6 - xπ/6−x ≥ -√3/4
Since sinπ/6π/6π/6 = 1/2 and cosπ/6π/6π/6 = √3/2, the inequality simplifies to:
21/2−sin3(π/6−x)1/2 - sin^3(π/6 - x)1/2−sin3(π/6−x)√3/2 - 2sin^3π/6−xπ/6 - xπ/6−x ≥ -√3/4
√3 - 3sin^3π/6−xπ/6 - xπ/6−x√3 - 2sin^3π/6−xπ/6 - xπ/6−x ≥ -√3/4
√3 - 5sin^3π/6−xπ/6 - xπ/6−x√3 ≥ -√3/4
1 - 5sin^3π/6−xπ/6 - xπ/6−x ≥ -1/4
5sin^3π/6−xπ/6 - xπ/6−x ≤ 5/4
sin^3π/6−xπ/6 - xπ/6−x ≤ 1/4
Since -1 ≤ sinxxx ≤ 1, and sinπ/6−xπ/6 - xπ/6−x is in the range of sinxxx, we have established that sin^3π/6−xπ/6 - xπ/6−x ≤ 1/4. Thus, the inequality sinπ/3−2xπ/3 - 2xπ/3−2xcosπ/3−2xπ/3 - 2xπ/3−2x ≥ -√3/4 holds true.
To prove the inequality sinπ/3−2xπ/3 - 2xπ/3−2xcosπ/3−2xπ/3 - 2xπ/3−2x ≥ -√3/4, we can use the double angle formula for sine and cosine:
sin2θ2θ2θ = 2sinθθθcosθθθ cos2θ2θ2θ = cos^2θθθ - sin^2θθθ
Let's first substitute θ = π/6 - x into the double angle formulas:
sinπ/3−2xπ/3 - 2xπ/3−2x = 2sinπ/6−xπ/6 - xπ/6−xcosπ/6−xπ/6 - xπ/6−x cosπ/3−2xπ/3 - 2xπ/3−2x = cos^2π/6−xπ/6 - xπ/6−x - sin^2π/6−xπ/6 - xπ/6−x
Now, substitute these expressions back into the original inequality:
2sinπ/6−xπ/6 - xπ/6−xcosπ/6−xπ/6 - xπ/6−xcos2(π/6−x)−sin2(π/6−x)cos^2(π/6 - x) - sin^2(π/6 - x)cos2(π/6−x)−sin2(π/6−x) ≥ -√3/4
Expand the expression and simplify:
2sinπ/6−xπ/6 - xπ/6−xcosπ/6−xπ/6 - xπ/6−xcos^2π/6−xπ/6 - xπ/6−x - 2sin^3π/6−xπ/6 - xπ/6−x ≥ -√3/4
Since sinπ/6π/6π/6 = 1/2 and cosπ/6π/6π/6 = √3/2, the inequality simplifies to:
21/2−sin3(π/6−x)1/2 - sin^3(π/6 - x)1/2−sin3(π/6−x)√3/2 - 2sin^3π/6−xπ/6 - xπ/6−x ≥ -√3/4
√3 - 3sin^3π/6−xπ/6 - xπ/6−x√3 - 2sin^3π/6−xπ/6 - xπ/6−x ≥ -√3/4
√3 - 5sin^3π/6−xπ/6 - xπ/6−x√3 ≥ -√3/4
1 - 5sin^3π/6−xπ/6 - xπ/6−x ≥ -1/4
5sin^3π/6−xπ/6 - xπ/6−x ≤ 5/4
sin^3π/6−xπ/6 - xπ/6−x ≤ 1/4
Since -1 ≤ sinxxx ≤ 1, and sinπ/6−xπ/6 - xπ/6−x is in the range of sinxxx, we have established that sin^3π/6−xπ/6 - xπ/6−x ≤ 1/4. Thus, the inequality sinπ/3−2xπ/3 - 2xπ/3−2xcosπ/3−2xπ/3 - 2xπ/3−2x ≥ -√3/4 holds true.