5x^2+9x=-4
:.5x+9x+4=0
:.(x+1)(5x+4)
:.x+1=0 and 5x+4=0
:.color(blue)(x=-1 and 5x=-4
:.color(blue)(x=-1 and color(blue)(x=-4/5
substitute color(blue)(x=-1
:.5(color(blue)(-1))^2+9(color(blue)(-1))=-4
:.5(color(blue)(-1))(color(blue)(-1))-9=-4
:.5-9=-4
:.color(blue)(-4=-4
substitute color(blue)(x=-4/5
:.5color(blue)((-4/5))^2+9(color(blue)(-4/5))=-4
:.5(color(blue)(-4/5))(color(blue)(-4/5))+9(color(blue)(-4/5))=-4
:.5(16/25)-(36/5)=-4
:.80/25-36/5=-4/1
:.(80-180=-100)/25
:.color(blue)(-100=-100