Question

(2a-7)(3-a)

Answer 1

(2a-7)(3-a)=6а-2а²-21+7а=13а-2а²-21=-2а²+13а-21

-2а²+13а-21=0

D= b 2 - 4ac = 1, D > 0 => 2 вещественных решения, √D = 1

x 1 = -b + √D/2а = -13 + 1/2 × (-2) =  3 ,

x 2 = -b - √D/2а = -13 - 1/2 × (-2) =  3,5