<span>0.25x2+0.8x−8=0 same as 5x^2+16-160=0 no obvious factors for rational roots, so use quadratic formula −(x−3)(x+9)=0 .... the factors are clearly (x-3) and (x+9), no need for formula 3x² = 9 ..... we see x^2=3, so roots are ± sqrt(3), no need for formula. −2x2+5x=7 .... here b^2<4ac, definitely use quadratic formula.</span>
