MHB Where Do Polar Curves r=5sin(theta) and r=5cos(theta) Intersect?

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The polar curves r=5sin(theta) and r=5cos(theta) intersect at points where 5sin(theta) equals 5cos(theta). Dividing both sides by 5cos(theta) leads to the equation tan(theta) = 1. This results in solutions for theta at π/4 and 5π/4 within the specified range. Substituting these values back into either equation gives the corresponding r values of 5√2/2 for both intersections. Thus, the points of intersection are (5√2/2, π/4) and (5√2/2, 5π/4).
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Determine the polar coordinates of the two points at which the polar curves r=5sin(theta) and r=5cos(theta) intersect. Restrict your answers to r >= 0 and 0 <= theta < 2pi.
 
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Aren't you going to at least attempt it yourself? r= 5 sin(theta)= 5 cos(theta). What do you get if you divide both sides by 5 cos(theta)?
 
There are probably loads of proofs of this online, but I do not want to cheat. Here is my attempt: Convexity says that $$f(\lambda a + (1-\lambda)b) \leq \lambda f(a) + (1-\lambda) f(b)$$ $$f(b + \lambda(a-b)) \leq f(b) + \lambda (f(a) - f(b))$$ We know from the intermediate value theorem that there exists a ##c \in (b,a)## such that $$\frac{f(a) - f(b)}{a-b} = f'(c).$$ Hence $$f(b + \lambda(a-b)) \leq f(b) + \lambda (a - b) f'(c))$$ $$\frac{f(b + \lambda(a-b)) - f(b)}{\lambda(a-b)}...

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