How do you graph r=4/(-3+3sintheta)r=43+3sinθ?

1 Answer
Oct 15, 2016

This is a hyperbola with its center (0, -4)(0,4); its vertices are at (0, -4 - sqrt(12)) and (0, -4 + sqrt(12))(0,412)and(0,4+12) and it opens downward and upward from its vertices.

Explanation:

Multiply both sides by the denominator:

4rsin(theta) - 3r = 44rsin(θ)3r=4

Multiply both side by -1:

3r - 4rsin(theta) = -43r4rsin(θ)=4

Move the sine term to the right:

3r = 4rsin(theta)-43r=4rsin(θ)4

Factor out a 4:

3r = 4(rsin(theta)-1)3r=4(rsin(θ)1)

Square both sides:

9r^2 = 16(rsin(theta)-1)^29r2=16(rsin(θ)1)2

Substitute x^2 + y^2x2+y2 for r^2r2 and yy for rsin(theta)rsin(θ)

9(x^2 + y^2) = 16(y - 1)^29(x2+y2)=16(y1)2

Expand the square on the right:

9(x^2 + y^2) = 16(y^2 - 2y + 1)9(x2+y2)=16(y22y+1)

distribute through the ()s:

9x^2 + 9y^2 = 16y^2 - 32y + 169x2+9y2=16y232y+16

Combine like terms and leave the constant on the right:

9x^2 - 4y^2 - 32y = 169x24y232y=16

Add -4k^24k2 to both sides:

9x^2 - 4y^2 - 32y -4k^2 = 16 - 4k^29x24y232y4k2=164k2

Factor out -4 from the y terms

9x^2 - 4(y^2 + 8y + k^2) = 16 - 4k^29x24(y2+8y+k2)=164k2

Use 8y to find the value of kk and k^2k2:

-2ky = 8y2ky=8y

k = -4, k^2 = 16k=4,k2=16

This makes the left a perfect square with k:

9x^2 - 4(y - -4)^2 = -489x24(y4)2=48

Divide both sides by -48:

(y - -4)^2/12 - 3/16x^2 = 1(y4)212316x2=1

Put in standard form:

(y - -4)^2/(sqrt(12))^2 - (x - 0)^2/(4sqrt(3)/3)^2 = 1(y4)2(12)2(x0)2(433)2=1

This is a hyperbola with its center (0, -4)(0,4) its vertices are at (0, -4 - sqrt(12)) and (0, -4 + sqrt(12))(0,412)and(0,4+12). It opens downward and upward from its vertices.