Question 166366
{{{(x - 4y)(5x - 9y)=(x)(5x)+(x)(-9y)+(-4y)(5x)+(-4y)(-9y)=5x^2-9xy-20xy+36y^2=5x^2-29xy+36y^2}}}


So {{{(x - 4y)(5x - 9y)=5x^2-29xy+36y^2}}}