jika tan x=1/t maka nilai 2 cos² x -1 adalah please bantuanyaaa

Trigonometri

tan A = 1/t
misal tan A = y/x
r² = x²+y²
r²= t²+ 1
r =  √(t²+1)

cos x = x/r = t/√(t²+1)

nilai 2 cos² A - 1 = 2 (t/√(t²+1))² -1
2 cos² A - 1 = [2 / {t²/(t²+1)}] - 1
2 cos² A - 1 = (2t²- t²-1)/(t²+1)
2 cos² A - 1 = (t² -1)/(t²+1)