83. No solution.

85. ${(x-2)}^2+48{(y-1)}^2=64$

87. ${\displaystyle \frac{\sqrt{7}}{4}}$

89. ${\displaystyle \frac{\sqrt{3}}{2}}$

91. ${\displaystyle \frac{\sqrt{2}}{2}}$

93. ${\displaystyle \frac{x^2}{9}}+{\displaystyle \frac{y^2}{8}}=1$

95. Points of intersection: $(-{\displaystyle \frac{17}{13}},-{\displaystyle \frac{3}{13}})$ and $(1,-1)$

97. Points of intersection: $(\sqrt{2},3\sqrt{2}),(\sqrt{2},-3\sqrt{2}),$

99. $y=-{\displaystyle \frac{8}{3}}x+{\displaystyle \frac{25}{3}}$

101. $12\pi$

103. $4\pi$

107. 4

109. ${\displaystyle \frac{10}{3}}$

111. ${\displaystyle \frac{x^2}{81}}+{\displaystyle \frac{y^2}{9}}=1$ or ${\displaystyle \frac{x^2}{9}}+{\displaystyle \frac{y^2}{81}}=1$