Usaremos a Lei dos cossenos:
[tex]R^2=a^2+b^2+2ab \cdot cos \alpha \\
2^2=1^2+(\frac{3}{2})^2+2.1.\frac{3}{2}\cdot cos \alpha \\
4=1+\frac{9}{4}+3 \cdot cos \alpha \\
4=\frac{13}{4}+3 \cdot cos \alpha \\
4-\frac{13}{9}=3 \cdot cos \alpha \\
\frac{23}{9}=3\cdot cos \alpha \\
cos \alpha = \frac{23}{27} \\
\alpha = arcsen \frac{23}{27}
[/tex]
