so I know that usually the income curve is equal to: $$x_1p_1 + x_2p_2 = m$$ if we rearrange this equation we get that the demand for good one ($x_1$) is equal to: $$x_1 = \frac{m-x_2p_2}{p_1}$$
None the less in my book it is said that:
The demand for good 1 is $x_1 = \frac {m}{(p_1 + p_2)}$
if anyone could explain me why $x_1 = \frac {m}{(p_1 + p_2)}$ instead of $x_1 = \frac{m-x_2p_2}{p_1}$ that would be greatly appreciated. many thanks in advance.