Question

Știe cineva să rezolve exercițiul 81??

Answer 1

B = sin(5x)/sin(x)-4cos(x)cos(3x)

x ≠ 0 => sin(x) ≠ 0

B•sin(x) = sin(5x)-4cos(x)cos(3x)sin(x)

B•sin(x) = sin(5x)-2sin(2x)cos(3x)

B•sin(x) = sin(5x)-2sin(2x)cos(3x)

B•sin(x) = sin(2x+3x)-2sin(2x)cos(3x)

B•sin(x) = sin(2x)cos(3x)+sin(3x)cos(2x)-2sin(2x)cos(3x)

B•sin(x) = sin(3x)cos(2x)-sin(2x)cos(3x)

B•sin(x) = sin(3x-2x)

B•sin(x) = sin(x)

B = sin(x)/sin(x)

B = 1 ∈ Q