Geometry

Quadrilaterals

Properties of Trapezoids (US) / Trapeziums (UK)

In the above diagram, quadrilateral A B C D ABCD 是一个trapezoid with A D B C . \overline{AD} \parallel \overline{BC}. If A B C = 60 , O C D = 20 , \lvert{\triangle ABC}\rvert=60, \lvert{\triangle OCD}\rvert=20, what is the area of O B C ? \triangle OBC ?

Note 1 1 :The above diagram is not drawn to scale, and A B C \lvert \triangle ABC \rvert denotes the area of A B C . \triangle ABC.
Note 2 2 :In the US a quadrilateral with one pair of parallel lines is called a "trapezoid." Elsewhere, a quadrilateral with one pair of parallel lines is called a "trapezium."

In the above diagram, quadrilateral A B C D ABCD 是一个trapezoid with A B C D . \overline{AB} \parallel \overline{CD}. If α = 73 \alpha^\circ={73}^\circ and γ = 135 , \gamma^\circ={135}^\circ, what is the value of ω β ? \omega-\beta ?

Note:In the US a quadrilateral with one pair of parallel lines is called a "trapezoid." Elsewhere, a quadrilateral with one pair of parallel lines is called a "trapezium."

In the above diagram, quadrilateral A B C D ABCD 是一个trapezoid with A D B C . \overline{AD} \parallel \overline{BC}. If A O : O C = 1 : 3 , O B C = 54 , \lvert{\overline{AO}}\rvert:\lvert{\overline{OC}}\rvert=1:3, \lvert{\triangle OBC}\rvert=54, what is the area of quadrilateral A B C D ? ABCD ?

Note 1 1 :The above diagram is not drawn to scale, and A B C \lvert{\triangle ABC}\rvert denotes the area of A B C . \triangle ABC.
Note 2 2 :In the US a quadrilateral with one pair of parallel lines is called a "trapezoid." Elsewhere, a quadrilateral with one pair of parallel lines is called a "trapezium."

In the above diagram, quadrilateral A B C D ABCD is an isosceles trapezoid with A D B C . \overline{AD} \parallel \overline{BC}. If l = 7 , α = 25 , β = 115 , l=7, \alpha^\circ={25}^\circ, \beta^\circ={115}^\circ, what is the value of x + y ? x+y ?

Note 1 1 :The above diagram is not drawn to scale.
Note 2 2 :In the US a quadrilateral with one pair of parallel lines is called a "trapezoid." Elsewhere, a quadrilateral with one pair of parallel lines is called a "trapezium."

Trapezium A B C D ABCD has A B AB parallel to D C DC . If D B C = 2 3 \angle DBC = 23 ^\circ and B C D = 5 9 \angle BCD = 59 ^\circ , what is A B D \angle ABD (in degrees)?

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