Умножаем
1) 2b*5a^4+2b*(-3b)-3b*10a^4-3b(-4b) =
= 10a^4b-6b^2-30a^4b+12b^2 =
= (10a^4b-30a^4b)+(12b^2-6b^2)
= -20a^4b+6b^2 = 6b^2-20a^4b
Умножаем
1) 2b*5a^4+2b*(-3b)-3b*10a^4-3b(-4b) =
= 10a^4b-6b^2-30a^4b+12b^2 =
= (10a^4b-30a^4b)+(12b^2-6b^2)
= -20a^4b+6b^2 = 6b^2-20a^4b