\( .x^{2}-3x^{2} \)

First, let's simplify the expression \( .x^{2}-3x^{2} \). The term \( .x^{2} \) can be interpreted as \( 0.1x^{2} \). Thus, we rewrite the expression as: \[ 0.1x^{2} - 3x^{2} = (0.1 - 3)x^{2} = -2.9x^{2}. \] So the simplified version is \( -2.9x^{2} \), which tells us that we're dealing with a downward-opening parabola when graphed! Now, if you ever encounter a problem like this, remember to combine like terms effectively and pay attention to the coefficients. It's a common mistake to overlook decimal points or neglect to factor out common elements, leading to unnecessary confusion. Double-check your calculations for a smoother solving experience!