Plane Geometry

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Triangle

 

triangle.png

 

Perimeter, P=a+b+c

Semi-perimeter, s=12P=12(a+b+c)

Sum of included angles, A+B+C=180

Area, A=12bh=12absinθ=s(sa)(sb)(sc)
 

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Quadrilateral

 

quadrilateral-sides.png

 

Perimeter, P=a+b+c+d

Semi-perimeter, s=12P=12(a+b+c+d)

Sum of included angles, A+B+C+D=360
 

quadrilateral-diagonals.png

 

Area, A=(sa)(sb)(sc)(sd)abcdcos2φ=12d1 d2sinθ

where, φ=12(A+C) or φ=12(B+D)
 

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Regular Polygons

 

regular-polygon.png

 

Perimeter, P=nx

Central angle of one segment, θ=360n

Area, A=nA1=n2xr=n2R2sinθ
 

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Circle

 

circle.png

 

Circumference, c=2πr=πd

Area, A=πr2=π4d2
 

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