How do you graph #r=4cos7theta#?

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Answer 1 · 2017-01-11T11:42:03

See the 7-petal rose and explanation.

#cos 7theta# is periodic, with period #(2pi)/7#.

#r = 4 cos 7theta >= 0 and <=4#

So, the complete rotation through #2pi# would create

7 petals @ 1 petal/period.

All these petals are contained in a square of side

2 (size of a petal) = 2 (4) = 8 units.

The cartesian form for #r = 4 cos 7theta# is

#(x^2+y^2)^2sqrt(x^2+y^2)=4(x^7-21x^5y^2+35x^3y^4-7xy^6)#

and this was used, for making the Socratic graph.

graph{(x^2+y^2)^4-4(x^7-21x^5y^2+35x^3y^4-7xy^6)=0 [-15, 15, -7.5, 7.5]}