(a+b)^2–2ab
123. (-------------------) • (a+b) =
a(a+b)
a^2+2ab+b^2–2ab
= ---------------------------- • (a+b) =
a(a+b)
(a^2+b^2)•(a+b) a^2+b^2
= ----------------------- = -------------
a(a+b) a
2ab+(a–b)^2
124. (-------------------) • b =
b(a–b)
2ab+a^2–2ab+b^2 (a^2+b^2)b
= --------------------------- • b = ---------------
b(a–b) b(a–b)
a^2+b^2
= -------------
a–b