![\displaystyle 1).. \sqrt{72}* \sqrt{2}= \sqrt{72*2}= \sqrt{144}=12 \\ \\ 2)..( \sqrt{17}- \sqrt{18})( \sqrt{17}+ \sqrt{18})=( \sqrt{17})^{2}-( \sqrt{18})^{2}=17-18=-1 \\ \\ 3).. \frac{ \sqrt{8}}{ \sqrt{18}}= \sqrt{ \frac{8}{18}}= \sqrt{ \frac{2*4}{2*9}}= \frac{2}{3} \sqrt{ \frac{2}{2}}= \frac{2}{3} \\ \\ 4).. \sqrt{45}- \sqrt{5}= \sqrt{5*9}- \sqrt{5}=3 \sqrt{5}- \sqrt{5}=2 \sqrt{5}](https://tex.z-dn.net/?f=%5Cdisplaystyle+1%29..+%5Csqrt%7B72%7D%2A+%5Csqrt%7B2%7D%3D+%5Csqrt%7B72%2A2%7D%3D+%5Csqrt%7B144%7D%3D12+%5C%5C++%5C%5C+2%29..%28+%5Csqrt%7B17%7D-+%5Csqrt%7B18%7D%29%28+%5Csqrt%7B17%7D%2B+%5Csqrt%7B18%7D%29%3D%28+%5Csqrt%7B17%7D%29%5E%7B2%7D-%28+%5Csqrt%7B18%7D%29%5E%7B2%7D%3D17-18%3D-1+%5C%5C++%5C%5C+3%29..+%5Cfrac%7B+%5Csqrt%7B8%7D%7D%7B+%5Csqrt%7B18%7D%7D%3D+%5Csqrt%7B+%5Cfrac%7B8%7D%7B18%7D%7D%3D+%5Csqrt%7B+%5Cfrac%7B2%2A4%7D%7B2%2A9%7D%7D%3D+%5Cfrac%7B2%7D%7B3%7D++%5Csqrt%7B+%5Cfrac%7B2%7D%7B2%7D%7D%3D+%5Cfrac%7B2%7D%7B3%7D+%5C%5C++%5C%5C+4%29..+%5Csqrt%7B45%7D-+%5Csqrt%7B5%7D%3D+%5Csqrt%7B5%2A9%7D-+%5Csqrt%7B5%7D%3D3+%5Csqrt%7B5%7D-+%5Csqrt%7B5%7D%3D2+%5Csqrt%7B5%7D+++++++++)
В третьем можно не вносить все под общий корень:
![\displaystyle 3).. \frac{ \sqrt{8}}{ \sqrt{18}}= \frac{ \sqrt{4*2}}{ \sqrt{9*2}}= \frac{2 \sqrt{2} }{3 \sqrt{2}}= \frac{2}{3}](https://tex.z-dn.net/?f=%5Cdisplaystyle+3%29..+%5Cfrac%7B+%5Csqrt%7B8%7D%7D%7B+%5Csqrt%7B18%7D%7D%3D+%5Cfrac%7B+%5Csqrt%7B4%2A2%7D%7D%7B+%5Csqrt%7B9%2A2%7D%7D%3D+%5Cfrac%7B2+%5Csqrt%7B2%7D+%7D%7B3+%5Csqrt%7B2%7D%7D%3D+%5Cfrac%7B2%7D%7B3%7D++++)
1)16+4=20(см)-длина 2-ой стороны
2)16+20+45=81(см)-длина всего четырёхугольника
X - y = - 3
2x + 7y = 3
••••••
7x - 7y = - 21
7x + 2x - 7y + 7y = - 21 + 3
9x = - 18
X = - 2
••••••••
- 2 - y = - 3
y = - 2 + 3
y = 1
X + y = - 2 + 1 = - 1
Формула площади круга: Sкр. = П, т.е., S = П * 26,01 = 26,01 П. Если продолжать и взять П как 3,14, то S = 26,01*3,14 = 81,6714.