y=x.
Let me explain.
y=x (the upper part) makes an angle of pi/4.
But if we consider the negative radius r, in polar coordinates we also get the lower part.
Thus we get a full line.
Hello, ^_^Engineer_Adam^_^!
Transform: .θ = π/4 to rectangular form.
Take the tangent of both sides: .tanθ .= .tan(π/4)
and we have: .tanθ .= .1
. . . . . . . . . . . ↓
. . . . . . . . . . . y
. . . . . .then:. .-- .= .1
. . . . . . . . . . . x
Therefore: .y .= .x