How do you convert (x + 1)^2 + (y + 1)^2 =4(x+1)2+(y+1)2=4 into polar form?

1 Answer
Dec 6, 2015

Substitute x = r cos thetax=rcosθ and y = r sin thetay=rsinθ into the equation to get:

(r cos theta + 1)^2 + (r sin theta + 1)^2 = 4(rcosθ+1)2+(rsinθ+1)2=4

Hence:

r^2 + 2(cos theta + sin theta)r - 2 = 0r2+2(cosθ+sinθ)r2=0

Explanation:

Substitute x = r cos thetax=rcosθ and y = r sin thetay=rsinθ into the equation to get:

(r cos theta + 1)^2 + (r sin theta + 1)^2 = 4(rcosθ+1)2+(rsinθ+1)2=4

This can be reformulated as follows:

4 = (r cos theta + 1)^2 + (r sin theta + 1)^24=(rcosθ+1)2+(rsinθ+1)2

= r^2 cos^2 theta + 2r cos theta + 1 + r^2 sin^2 theta + 2r sin theta + 1=r2cos2θ+2rcosθ+1+r2sin2θ+2rsinθ+1

= r^2 (cos^2 theta + sin^2 theta) + 2r (cos theta + sin theta) + 2=r2(cos2θ+sin2θ)+2r(cosθ+sinθ)+2

= r^2 + 2r (cos theta + sin theta) + 2=r2+2r(cosθ+sinθ)+2

Subtract 44 from both ends to get:

r^2 + 2(cos theta + sin theta)r - 2 = 0r2+2(cosθ+sinθ)r2=0