Figure shows three vectors $\overrightarrow{\mathrm{a}},\overrightarrow{\mathrm{b}} \mathrm{and} \overrightarrow{\mathrm{c}}$, where R is the midpoint of PQ. Then which of the following relations is correct?

1st method : From fig
$\begin{array}{l}\overline{\mathrm{C}}=\overline{\mathrm{a}}+\overline{\mathrm{PR}}\dots \dots \left(1\right)\\ \overline{\mathrm{C}}=\overline{\mathrm{b}}+\overline{\mathrm{QR}}\dots \dots \left(2\right)\\ \text{ but }\overline{\mathrm{PR}}=-\overline{\mathrm{QR}}\end{array}$
equation (1) + equation (2)
$\overline{\mathrm{a}}+\overline{\mathrm{b}}=2\overline{\mathrm{c}}$
2nd method : From figure
$\begin{array}{l}\overline{\mathrm{b}}+\overline{\mathrm{a}}=\overline{\mathrm{OS}}=2\left(\overline{\mathrm{OR}}\right)\\ \Rightarrow \overline{\mathrm{a}}+\overline{\mathrm{b}}=2\overline{\mathrm{c}}\end{array}$