Diketahui tan A =4t. Tentukan cos 2A

Trigonometri

tan A = 4t --> y/x = 4t/1
r² = x²+y²
r² = 16t² + 1
r = √(16t²+1)

sin A  = y/r = (4t)/√(16t²+1)
cos 2 A = 1 - 2 sin² A
cos 2A = 1 - 2 {16t² /(16t²+ 1)}
cos 2A = 1-  32t²/(16t²+1)
cos 2A = (16t² + 1 - 32t²)/(16t² + 1)
cos 2A = (1 - 16t²)/(16t² +1)
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