4x^2+11x-20=4(x-b)(x+4) найдите b

4x^2+11x-20=4(x-b)(x+4)D=121-4*4*(-20)=441=21^2x1=-11-21/8=-4x2=-11+21/8=5/44(x-x2)(x-x1)4*5/4=5b=5