Intermediate Algebra (12th Edition)

$0.05y^2+1.01y-0.84$
Using $(a+b)(c+d)=ac+ad+bc+bd$ or the FOIL Method, the product of the binomials in the given expression, $(0.1y+2.1)(0.5y-0.4) ,$ is \begin{array}{l}\require{cancel} 0.1y(0.5y)+0.1y(-0.4)+2.1(0.5y)+2.1(-0.4) \\\\= 0.05y^2-0.04y+1.05y-0.84 \\\\= 0.05y^2+1.01y-0.84 .\end{array}