[tex]a_{17}+a_{14}=-202\\\\a_{17}=a_1+16r\\a_{14}=a_1+13r\\\\a_1+16r+a_1+13r=-202\\2a_1+29r=-202 /-29r\\2a_1=-202-29r\\\\a_{48}+a_{77}=-372\\a_{48}=a_1+47r\\a_{77}=a_1+76r\\\\a_1+47r+a_1+76r=-372\\2a_1+123r=-372\\-202-29r+123r=-372\\-29r+123r=-372+202\\94r=-170 /:94\\r=-\frac{170}{94}=-\frac{85}{47}\\\\a_{39}+a_{54}=a_1+38r+a_1+53r=2a_1+91r=-202-29r+91r=-202+62r=-202+62*(-\frac{85}{47})=-202+(-\frac{5270}{47})=-202-\frac{5270}{47}=-202-112\frac6{47}=-314\frac6{47}[/tex]
