A) X^2-7x+12
D) X^2-2x-63

а) х²-7х+12=0 
а=1; b= -7; с=12 
D=b²-4ac=(-7)²-4*1*12=49-48=1 
√D=√1=1 
x₁ = (-b-√D)/2a = (7-1)/2 = 3 
x₂ = (-b+√D)/2a = (7+1)/2 = 4 

d) D=4+252=256
√D=16 
x₁ = (2-16)/2 = -7 
x₂ = (2+16)/2 = 9