6. Вычислите интеграл ∫(от π/4 до π) 4cos(2x/3) dx

∫(от π/4 до π) 4cos(2x/3) dx = 4 * [3/2 sin(2x/3)](от π/4 до π) = 6 * [sin(2x/3)](от π/4 до π) = 6 * (sin(2π/3) - sin(2(π/4)/3)) = 6 * (sin(2π/3) - sin(π/6)) = 6 * (√3/2 - 1/2) = 3√3 - 3.