experts and my dear friends can u help mr to solve 74 and 75 que with easiest method.:

74. If x+y+z=10 and x²+y²+z²=52 te value of xy+yz+zx will be -
(A) 20             (B) 26
(C) 24             (D) 12

75. The value of $$\begin{gathered} \frac{1}{1+{\mathrm{x}}^{\mathrm{a}-\mathrm{b}}+{\mathrm{c}}^{\mathrm{c}-\mathrm{b}}}+\frac{1}{1+{\mathrm{x}}^{\mathrm{b}-\mathrm{c}}+{\mathrm{x}}^{\mathrm{a}-\mathrm{c}}}+\frac{1}{1+{\mathrm{x}}^{\mathrm{c}-\mathrm{a}}+{\mathrm{x}}^{\mathrm{b}-\mathrm{a}}}- \\ \left(\mathrm{A}\right) \frac{1}{3} \left(\mathrm{B}\right) \frac{2}{3} \\ \left(\mathrm{C}\right) 2 \left(\mathrm{D}\right) 1 \end{gathered}$$