Diketahui tan2A =2m/1-m²maka cos 2A?

TriGonoMetRi

tan 2A = 2tan A /(1 - tan² A)

tan 2A = 2m / (1 - m²)
tan A = m

r = √(m² + 1)

cos A = 1/√(1 + m²)
cos 2A = 2 cos² A - 1
cos 2A = 2/(1 + m²) - 1
cos 2A = (2 - (1 + m²))/(1 + m²)
cos 2A = (1 - m²)/(1 + m²)