Answer: 7 units
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Step-by-step explanation:
r = distance from the origin (0,0) to a point on the polar curve
To find the length of the flower petal, we need to max out r (i.e. get it as large as possible).
Recall that sin(x) maxes out at 1, so that also applies to sin(2θ) as well.
Therefore, r = 7*sin(2θ) maxes out at r = 7*1 = 7 and this is the length of each petal. Basically it's the number out front of the sine term.
The graph is shown below. To type the symbol θ into desmos, you need to type "theta" without quotes.