Answer:
cos-1(-4/14)
Step-by-step explanation:
If
4.5=r
3.5=s
2=t
By law of cosines:
[tex]r^{2}=s^{2}+t^{2} -2st cosR\\\\CosR= \frac{r^{2} -s^{2} -t^{2} }{-2st} \\\\R=cos^{-1} (\frac{(4.5)^{2}-3.5^{2} -2^{2} }{-2(3.5)(2)} )\\R= cos^{-1} (-\frac{4}{14} )[/tex]
