$$\text { Compute the quadratic form } x ^ { T } A x \text { for the given matrix } A \text { and vector } x \text {. }$$

Multiple Choice

$$\text { Compute the quadratic form } x ^ { T } A x \text { for the given matrix } A \text { and vector } x \text {. }$$
- $$A = \left[ \begin{array} { r r } 2 & 0 \\0 & - 9\end{array} \right] , x = \left[ \begin{array} { l } x _ { 1 } \\x _ { 2 }\end{array} \right]$$

A) $2 x { } _ { 1 } ^ { 2 } - 9 x \frac { 2 } { 2 }$
B) $2 x _ { 1 } - 9 x _ { 2 }$
C) $4 x1 - 18 x 2$
D) $- 9 x \frac { 2 } { 1 } + 2 x \frac { 2 } { 2 }$