1. The problem is to find the decimal value of the expression $\frac{1}{2} \sqrt{2} - \sqrt{2}$. 2. Recall that $\sqrt{2}$ is the square root of 2, approximately equal to 1.414. 3. First, calculate $\frac{1}{2} \sqrt{2}$ which is half of $\sqrt{2}$: $$\frac{1}{2} \times 1.414 = 0.707.$$ 4. Now subtract $\sqrt{2}$ from this value: $$0.707 - 1.414 = -0.707.$$ 5. So, the decimal form of $\frac{1}{2} \sqrt{2} - \sqrt{2}$ is approximately $-0.707$. 6. This means on your calculator, you can enter the expression as (1/2)*sqrt(2) - sqrt(2) to get about -0.707.