Calculate the mass fraction of the solute in solutions consisting of 200 g of water and 5 g of NaCLX.

We start solving the equation x (x + 2) – (x – 3) (x + 3) = 13 by opening the parentheses.

First of all, we apply the rule of multiplication of a monomial by a polynomial, as well as the formula for abbreviated multiplication of the difference of squares:

(a – b) (a + b) = a ^ 2 – b ^ 2.

And also apply the rule of opening parentheses before which there is a minus.

Open the brackets and get the equation:

x * x + x * 2 – (x ^ 2 – 9) = 13;

x ^ 2 + 2x – x ^ 2 + 9 = 13;

We transfer 9 to the right side and give similar ones:

x ^ 2 – x ^ 2 + 2x = 13 – 9;

2x = 4;

x = 2.