Advanced geometry problem

Geometry Level pending

Orange shape of a size 5.655 cm^2 is making one fifth of the area of a cricle and |PR| = 1.4 cm. Calculate the area of the blue circle segment using following rules: 1. Every result round up to 3 signifficant digits 2. Use Pi button on a calculator or (3.141592654)


The answer is 0.236.

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1 solution

Tomáš Hauser
Jun 21, 2018

Since we know that orange shape is making one fifth of the area of a cricle, we can calculate its radius: S E O P = 1 5 × S C S C = 5 × 5.655 = 28.274 c m 2 S C = π × r 1 2 r 1 = S C π = 28.274 π \buildrel . = 3 c m 2 \begin{array}{l} {S_{EOP}} = \frac{1}{5} \times {S_C}\\ {S_C} = 5 \times 5.655 = 28.274{\rm{ }}c{m^2}\\ {S_C} = \pi \times r_1^2 \Rightarrow {r_1} = \sqrt {\frac{{{S_C}}}{\pi }} = \sqrt {\frac{{28.274}}{\pi }} \buildrel\textstyle.\over= 3{\rm{ }}c{m^2} \end{array} We can notice that: r 1 = b {r_1} = b c a = r 1 P R = 3 1.4 = 1.6 c m {c_a} = {r_1} - \left| {PR} \right| = 3 - 1.4 = 1.6{\rm{ }}cm By using Pythagorean theorem, we can calculate a height from the point C : v c = b 2 c a 2 = 3 2 1.6 2 = 2.538 c m {v_c} = \sqrt {{b^2} - {c_a}^2} = \sqrt {{3^2} - {{1.6}^2}} = 2.538{\rm{ }}cm By using Euclid's formula, we can calculate 2nd part of the side c : v c 2 = c a × c b c b = v c 2 c a = 2.538 2 1.6 = 4.026 c m v_c^2 = {c_a} \times {c_b} \Rightarrow {c_b} = \frac{{v_c^2}}{{{c_a}}} = \frac{{{{2.538}^2}}}{{1.6}} = 4.026{\rm{ }}cm Via trigonometric formula for sin , we can calculate angle beta : sin ( β ) = b c β = arcsin ( b c ) = arcsin ( 3 4.026 + 1.6 ) = 32.2 \sin \left( \beta \right) = \frac{b}{c} \Rightarrow \beta = \arcsin \left( {\frac{b}{c}} \right) = \arcsin \left( {\frac{3}{{4.026 + 1.6}}} \right) = 32.2 We can tell, that: β = δ \beta = \delta Where delta is XBY angle and also for the radius of a 2nd circle: r 2 = c b {r_2} = {c_b} Our last step involves a formula for a circle segment: S = 1 2 × r 2 2 ( π × δ 180 sin ( δ ) ) = 1 2 × 4.02 6 2 ( π × 32.2 180 sin ( 32.2 ) ) = 0.236 c m 2 S = \frac{1}{2} \times r_2^2\left( {\frac{{\pi \times \delta }}{{180}} - \sin \left( \delta \right)} \right) = \frac{1}{2} \times {4.026^2}\left( {\frac{{\pi \times 32.2}}{{180}} - \sin \left( {32.2} \right)} \right) = 0.236{\rm{ }}c{m^2}

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