Question

covert to rectangular form r=sec@/(1+tan@)

Answer 1

Simplify the RHS first:
\[\Large r=\frac{\frac{1}{\cos\theta}}{1+\frac{\sin\theta}{\cos\theta}}=\frac{1}{\cos\theta+\sin\theta}\\
\Large r(\cos\theta+\sin\theta)=1\\
\Large r\cos\theta+r\sin\theta=1\\
\Large x+y=1\]