[tex]\displaystyle 36x^2-84x+49=0 \\ a=36,b=-84,c=49 \\ \Delta=b^2-4ac=(-84)^2-4 \cdot 36 \cdot 49=7056-7056=0 \\ x_1=x_2=- \frac{b}{2a}=- \frac{-84}{2 \cdot 36} = - \frac{-84}{72}=-\left(- \frac{84}{72} \right)=-\left(- \frac{7}{6} \right)= \frac{7}{6} [/tex]
