Cho các vectơ a ,b . Khẳng định nào sau đây là đúng?

A. ${\left(\overrightarrow{a}+\overrightarrow{b}\right)}^2={\overrightarrow{a}}^2+{\overrightarrow{b}}^2$

B.${\left(\overrightarrow{a}+\overrightarrow{b}\right)}^2={\overrightarrow{a}}^2-2\overrightarrow{a}.\overrightarrow{b}+{\overrightarrow{b}}^2$

C. ${\left(\overrightarrow{a}+\overrightarrow{b}\right)}^2={\overrightarrow{a}}^2+2\overrightarrow{a}.\overrightarrow{b}+{\overrightarrow{b}}^2$

D.${\left(\overrightarrow{a}+\overrightarrow{b}\right)}^2=-{\overrightarrow{a}}^2+2\overrightarrow{a}.\overrightarrow{b}-{\overrightarrow{b}}^2$