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ruas kiri
{(cos² x + sin² x)(cos² x - sin² x)}/{(1- tan²x)(1+tan² x)}=
={(cos² x+ sin²x)(cos² x - sin² x)}/ {(cos² x-sin² x)(cos² x +sin² x)/(cos⁴ x)}
={ (1)(cos² x - sin²x)}/ (cos²x -sin² x)(1) / (cos⁴ x)
= 1 / (1/ cos⁴ x)
= cos⁴ x
Matematika SMA Kelas XI
Pembuktian identitas
⇔ [cos⁴θ - sin⁴θ] / [1 - tan⁴θ] = cos⁴θ
⇔ [cos⁴θ - sin⁴θ] / [1 - (sin⁴θ/cos⁴θ )] = cos⁴θ
⇔ [cos⁴θ - sin⁴θ] [cos⁴θ] / [cos⁴θ - sin⁴θ] = cos⁴θ
⇔ cos⁴θ = cos⁴θ
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