Simplify the given algebraic expression. \[ 3 x^{2}-7 x^{2} \] \[ 3 x^{2}-7 x^{2}= \]

Step 1 ：The given algebraic expression is \(3 x^{2}-7 x^{2}\).

Step 2 ：This is a subtraction of two terms with the same variable part, i.e., \(x^{2}\).

Step 3 ：In such cases, we can simply subtract the coefficients of the like terms to simplify the expression.

Step 4 ：The coefficient of the first term is 3 and the coefficient of the second term is 7.

Step 5 ：Subtracting the coefficients, we get -4.

Step 6 ：So, the simplified form of the given algebraic expression is \(\boxed{-4x^{2}}\).