(1)y=4x^2-24x+26
y=4(x^2-6x)+26
=4(x^2-6x+9-9)+26
=4(x^2-6x+9)-4*9+26
=4(x-3)^2-10
(2)y=-1/4x^2+x+4
y=-0.25(x^2-4x)+4
=-0.25(x^2-4x+4)-(-4)*0.25+4
=-1/4(x-2)^2+5
(3)y=(x+2)(1-2x)
y=-[(x+2)(2x-1)]
=-(2x^2-x+4x-2)
=-(2x^2+3x-2)
=-2(x^2+1.5x-1)
=-2(x^2+1.5x+(3/4)^2-(3/4)^2-1)
=-2[(x+3/4)^2-25/16]
=-2(x+3/4)^2+25/8