Lösung 2.1:2a

First, multiply the brackets together. In the first product, every term in the first bracket is multiplied by every term in the second bracket,

(x−4)(x−5)−3x(2x−3)=xx−x5−4x−4(−5)−(3x2x−3x3)=x2−5x−4x+20−(6x2−9x)=x2−5x−4x+20−6x2+9x

Then, gather together x2−x− and the constant terms and simplify

=(x2−6x2)+(−5x−4x+9x)+20=−5x2+0+20=−5x2+20