найти точки экстремума функции двух независимых переменных z=f(x,y) z=2x^2+3xy+y^2-yx

почему в ответе получается 26? 

 ПОМОГИТЕ ПОЖАЛУУЙСТА СРОЧНО НУЖНО! Переделайте предложения из действительного залога в
страдательный, сохраняя видовременную форму сказуемого. Напишите и
переведите полученные предложения на русский язык.
1. I clean the room every day.
2. This firm is constantly producing irrigation systems.
3. A famous architect has designed this cathedral.
4. They sent a message yesterday.
5. I will remember this rule.

 Выпишите из текста предложения с глаголами в форме причастия или герундия или сослагательном наклонении.

Types of Loading

        As to the manner in which loads are applied or transmitted to a structure of machine they may be considered as static loads, repeated loads, impact and energy loads.

       1 .In static, steady or dead loads are forces that are applied slowly and remain nearly constant after being applied to the body such as the loads on most buildings or the load applied to a bar in the usual type of testing machine.

       Other Classifications of Loads.-Loads may be classified as distributed loads and concentrated loads. A distributed load may be uniformly distributed or non-uniformly distributed. A concentrated load is one whose area of contact with the resisting body is negligible in comparison with the area of the resisting body.

II. Write out from the text the sentences with verbs in the form of the Participle or the Gerund or the Subjunctive mood.

продефенцировать

s(t)=t^3/3+4t^2-1 , u(2)