Answer:
The answer is the second one ⇒ he should write cosФ = cos²Ф/cosФ to find a common denominator
Step-by-step explanation:
∵ tanФ = sinФ/cosФ
∴ (sinФ/cosФ) (sinФ) + cosФ
∵ cosФ = cos²Ф/cosФ
∴ (sin²Ф/cosФ) + cosФ = (sin²Ф/cosФ) + (cos²Ф/cosФ)
∴ = (sin²Ф + cos²Ф)/cosФ
∵ sin²Ф + cos²Ф = 1
∴ tanФ sinФ + cosФ = 1/cosФ = secФ
