13.1-bo'lim : Limitlar
2. Quyidagi limitni hisoblang.
\[\mathop {\lim }\limits_{\left( {x,y} \right) \to \left( {2,1} \right)} \frac{{{x^2} - 2xy}}{{{x^2} - 4{y^2}}}\]Yechim
Xo‘sh, bu muammo bilan biz nuqtani qo'ysak, surat va maxrajda nolga ega bo‘lishini ko‘rishimiz mumkin. Biroq, bu turdagi misollarning ko'pchiligidan farqli o'laroq, bu shunchaki limit mavjud emas degani emas.
Bunday holda, biz funktsiyani quyidagi tarzda ko'paytuvchilarga ajratish va soddalashtirishimiz mumkinligiga e'tibor bering,
\[\mathop {\lim }\limits_{\left( {x,y} \right) \to \left( {2,1} \right)} \frac{{{x^2} - 2xy}}{{{x^2} - 4{y^2}}} = \mathop {\lim }\limits_{\left( {x,y} \right) \to \left( {2,1} \right)} \frac{{x\left( {x - 2y} \right)}}{{\left( {x - 2y} \right)\left( {x + 2y} \right)}} = \mathop {\lim }\limits_{\left( {x,y} \right) \to \left( {2,1} \right)} \frac{x}{{x + 2y}}\]Biz bu turdagi ko'phadlarni ko'paytuvchilarga ajratishga odatlanmagan bo'lishimiz mumkin, lekin ko'paytuvchilarga ajratish hali ham bu limitlarni hisoblashimiz kerak bo'lgan imkoniyat ekanligini unutmasligimiz kerak.
2-qadam
Endi biz funktsiyani ko'paytuvchilarga ajratdik va soddalashtirdik, biz nolga bo'linishni yo'qotganimizni ko'ramiz va endi limitni hisoblashimiz mumkin. Shunday qilib,
\[\mathop {\lim }\limits_{\left( {x,y} \right) \to \left( {2,1} \right)} \frac{{{x^2} - 2xy}}{{{x^2} - 4{y^2}}} = \mathop {\lim }\limits_{\left( {x,y} \right) \to \left( {2,1} \right)} \frac{x}{{x + 2y}} = \require{bbox} \bbox[2pt,border:1px solid black]{{\frac{1}{2}}}\]