Hi,
a) (a-3)(a+5) = a^2+5a-3a-15 = a^2+2a-15
b) (3x-y)(4x+5y) = 12x^2+15xy-4xy-5y^2 = 12x^2+11xy-5y^2
c) (1/2a-1/4)(1/3-1/4a) = 1/6a - 1/8a^2 - 1/12 + 1/16a = -1/8a^2-1/12 + 11/48a
d) (b-3)(b+2-2c) = b^2 + 2b - 2bc - 3b - 6 + 6c = b^2 - b -2bc -6 + 6c
Grüße