تست

$$

begin{align*}

  & phi(x,y) = phi left(sum_{i=1}^n x_ie_i, sum_{j=1}^n y_je_j right)

  = sum_{i=1}^n sum_{j=1}^n x_i y_j phi(e_i, e_j) =

  & (x_1, ldots, x_n) left( begin{array}{ccc}

      phi(e_1, e_1) & cdots & phi(e_1, e_n)

      vdots & ddots & vdots

      phi(e_n, e_1) & cdots & phi(e_n, e_n)

    end{array} right)

  left( begin{array}{c}

      y_1

      vdots

      y_n

    end{array} right)

end{align*}

$$

[x = {-b pm sqrt{b^2-4ac} over 2a}.]

When (a ne 0), there are two solutions to (ax^2 + bx + c = 0) and they are [x = {-b pm sqrt{b^2-4ac} over 2a}.]

\[x = {-b \pm \sqrt{b^2-4ac} \over 2a}.\]