91.The two vectors A and B are drawn from a common point, and C=A+B, (a) Show that if $\boldsymbol{C}^{2}=\boldsymbol{A}^{2}+\boldsymbol{B}^{2}$ the angle between the vectors $\overrightarrow{\boldsymbol{A}}$ and $\overrightarrow{\boldsymbol{B}}$ is $90^{\circ}$. (b) Show that if $C^{2}<A^{2}+B^{2}$, the angle between the vectors $\vec{A}$ and $\vec{B}$ is greater than $90^{\circ}$ (c) Show that if $C^{2}>A^{2}+B^{2}$, the angle between the vectors $\vec{A}$ and $\vec{B}$ is between $0^{\circ}$ and $90^{\circ}$.

 91.The two vectors A and B are drawn from a common point, and C=A+B, (a) Show that if $\boldsymbol{C}^{2}=\boldsymbol{A}^{2}+\boldsymbol{B}^{2}$ the angle between the vectors $\overrightarrow{\boldsymbol{A}}$ and $\overrightarrow{\boldsymbol{B}}$ is $90^{\circ}$. (b) Show that if $C^{2}<A^{2}+B^{2}$, the angle between the vectors $\vec{A}$ and $\vec{B}$ is greater than $90^{\circ}$ (c) Show that if $C^{2}>A^{2}+B^{2}$, the angle between the vectors $\vec{A}$ and $\vec{B}$ is between $0^{\circ}$ and $90^{\circ}$.