As shown in the diagram, using 2 straight cuts from the same starting point on the perimeter, I've cut a circular pizza into 3 pieces of equal areas. However, each of the 2 identical pieces at the top and bottom has more crust than the middle piece!
A slice with larger crust has X % more crust than the slice with smaller crust.
Assuming the crust of the pizza is 1-dimensional, find X to the nearest integer.
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Solving x numerically using Python
Hi, how did you know that the area of ABO and ACO are each sinx*cosx?
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I've added a picture for clarification. Since the radius is 1 , the legs of the right triangle are sin x and cos x .
Or, once you found x, you could have used the formula for the arc length of a sector to derive arcBC, and then the other two arcs as well and then figured out the answer from there. But very good solution.
I thought the point of the question was calculating x.
So, this was to be a numerical guesswork solution... Was there any specific way to solve a hybrid equation involving trigonometric and algebraic functions??
We can break up the middle piece as follows, where A C and A D are the two cuts, O is the center of the pizza circle, A B is the diameter, x is the measurement of ∠ B O C , and r is the radius of the pizza circle.
Then the area of sector B C is A s e c t o r = 2 π x π r 2 = 2 x r 2 , and the area of △ A O B is A △ = 2 1 r 2 sin ( π − x ) = 2 1 r 2 sin ( x ) . By symmetry, the area of sector B D is the same as the area of sector B C and the area of △ A O D is the same as the area of △ A O B .
Since all of these parts must add to one third the area of the circle, we have 3 1 π r 2 = 2 ( 2 x r 2 + 2 1 r 2 sin ( x ) ) , which simplifies to π = 3 sin ( x ) + 3 x . Solving numerically gives x ≈ 0 . 5 3 6 2 6 6 9 8 .
Since the crust of the upper slice is π − x , and the crust of the middle slice is 2 x , its percent increase is 2 x π − x − 2 x ⋅ 1 0 0 % ≈ 1 4 3 % .
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My solution solves pi = 3 sin x + 3x, not pi = 3 cos x sin x + 3x
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My bad! I will fix original instead of reposting here. Tx for pointing that out
My solution x ~= 0.586311970336 is incorrect and correctly pointed out by David x ~= 0.536266978989 as shown in solution above.
Calling 2 θ the angle of the smallest arch seen by the centre of the pizza, expressing the area of the central slice as function of θ reduces to solving numerically θ + sin θ = 3 π
I've done this iteratively
θ 0 = 3 π
θ i + 1 = 2 θ i + π / 3 − sin θ i
After 9 iterations this gives 0.536266979
The rest is straightforward, X = 2 θ π − 3 θ ∗ 1 0 0 = 1 4 3
The area of the top piece is the area of a segment of a circle. This can be found by taking the area of the sector that contains it and subtracting the area of the triangle in that same sector. Let's call the central angle of this sector measured in radians x. Area of sector
1/2 x * r^2
Area of triangle
1/2 * 2 sin(x/2) * cos(x/2) * r^ 2=
1/2 sin(x) r^2
Let's say r = 1 to simplify calculations The area of this segment has to be equal to 1/3 of the total area, which is pi/3
Area of sector - Area of triangle
x - sin(x) = 2pi/3
x approximately = 2.605 The crust of this segment is x And the crust of the large segment is 2pi - 2x Solving for both of these, finding the percent increase, and rounding to the nearest integer gives
143
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Assume the pizza has radius 1 .
We can find that 4 ∗ ∠ B A O = ∠ B O C from inscribed angles. The area of the isosceles triangles △ A B O and △ A C O are each sin x cos x which can be found by dividing them into two smaller right triangles with hypotenuse 1 (see below). Using the sector area formula, the area of sector B C O is 2 1 4 x ∗ 1 2 = 2 x . Therefore, 2 sin x cos x + 2 x = 3 π . Solving this gets x ≈ 0 . 2 6 8 1 3 3 , so ∠ B O C = 4 x ≈ 1 . 0 7 2 5 3 4 . We find that ∠ B O A = ∠ C O A ≈ 2 . 6 0 5 3 2 6 ≈ 1 4 3 % larger than ∠ B O C , and the same perecentage applies to the crust of each slice.
Here, D O = sin x and A B = 2 cos x , so the area is 2 1 sin x ∗ 2 cos x = sin x cos x .