a,b −− wymiary prostokąta
P(prostokąta)= a*b= PΔAPD+ PΔBPC+ PΔAPB+ PΔDCP
h1+h2= b i h3 + h4= a
| 1 | 1 | 1 | 1 | |||||
PΔAPD+ PΔBPC= | b*h4 + | b*h3= | b( h4+h3) = | a*b
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| 2 | 2 | 2 | 2 |
| 1 | 1 | 1 | 1 | |||||
PΔAPB+ PΔDCP= | *a*h2+ | *a*h1= | a( h1+h2) = | a*b
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| 2 | 2 | 2 | 2 |
| 1 | ||
P(prostokąta) = 2* | a*b= a*b
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| 2 |