Question 320415
Use a substitution,
{{{A=2u-5}}}
{{{B=-5u+3}}}
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{{{(5x+2u-5)(4x-5u+3)=(5x+A)(4x+B)}}}
{{{(5x+2u-5)(4x-5u+3)=20x^2+5Bx+4Ax+AB}}}
{{{(5x+2u-5)(4x-5u+3)=20x^2+(5B+4A)x+AB}}}
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{{{5B+4A=5(-5u+3)+4(2u-5)}}}
{{{5B+4A=-25u+15+8u-20}}}
{{{5B+4A=-17u-5}}}
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{{{AB=(2u-5)(-5u+3)}}}
{{{AB=-10u^2+6u+25u-15}}}
{{{AB=-10u^2+31u-15}}}
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Substituting,
{{{(5x+2u-5)(4x-5u+3)=20x^2+(5B+4A)x+AB}}}
{{{(5x+2u-5)(4x-5u+3)=20x^2+(-17u-5)x-10u^2+31u-15}}}
{{{(5x+2u-5)(4x-5u+3)=highlight(20x^2-(17u+5)x-10u^2+31u-15)}}}