5 ⋅ 4 2 = 5 ⋅ 16 = 80 ( 5 ⋅ 4 ) 2 = 20 2 = 400 ( 5 − 4 ) 2 = 1 2 = 1 5 ⋅ ( 5 − 4 ) 2 = 5 ⋅ 1 2 = 5 ⋅ 1 = 5 4 ⋅ 5 2 − 5 ⋅ 4 2 = 4 ⋅ 25 − 5 ⋅ 16 = 100 − 80 = 20
100 ⋅ a 2 ; 40 a
3 a ⋅ 5 a = 15 ⋅ a 2
De oppervlakte is 37.500 en de omtrek is 800.
De oppervlakte is 150.000 en de omtrek is 1600.
Zie opgave a.
Die van 2 a bij 4 a . De omtrek is 12 a .
Die van 2 a bij 2 a . De oppervlakte is 4 a 2
5 a ⋅ 5 a = 25 a 2 a ⋅ 5 a = 5 ⋅ a 2
Zie antwoord opgave 24a.
( 4 a ) 2 = 4 a ⋅ 4 a = 16 a 2
De volgende gelijkheden zijn juist: 5 a 2 = a ⋅ 5 a ( 5 a ) 2 = 5 a ⋅ 5 a ( 5 a ) 2 = 25 a 2
11 a 2 + 3 a 2 = 14 a 2
3 ⋅ 5 2 + 2 ⋅ 5 ⋅ 4 = 3 ⋅ 25 + 40 = 115
10 2 + 10 = 110
De gelijkheid is dus fout. Immers als bijvoorbeeld b = 2 dan: 3 ⋅ ( 5 b ) 2 = 3 ⋅ 10 2 = 3 ⋅ 100 = 300 en ( 15 b ) 2 = ( 30 ) 2 = 900 .
3 a 2 + 5 a 2 = 8 a 2 3 a + 5 a = 8 a 3 a ⋅ 5 a = 15 a 2 of 3 ⋅ 5 a = 15 a of 3 a ⋅ 5 = 15 a .