Find the value range of independent variable x in quadratic function y = x + 3 / X

Find the value range of independent variable x in quadratic function y = x + 3 / X

The denominator cannot be 0, so x is not equal to 0

Generally, the value range of independent variable x in quadratic function is_____

R (all real numbers)

The value range of independent variable in practical problems of quadratic function
At the beginning, a businessman sold a certain commodity with a purchase price of 8 yuan per piece at 10 yuan per piece, and he could sell 100 pieces per day. He wanted to increase the selling price to increase the profit. Through the experiment, it was found that every 1 yuan increase in the price of this commodity would reduce the daily sales by 10 pieces. 1. Write the functional relationship between the daily profit y (yuan) and the selling price x (yuan / piece);

y=1000,(x=10)
y=[100-10(x-10)]x,(x>10)
Just put them together in braces