Решите неравенство: 2^(x/(x+1))-2^((5x+3)/(x+1))+8≤2^((2x)/(x+1))

Лебедев Дмитрий Сергеевич

Учитель математики

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Решением неравенства является множество x(,-1)[0,+)x is an element of open paren negative infinity comma negative 1 close paren union open bracket 0 comma positive infinity close paren. Шаг 1: Преобразование показателей степеней Выразим все показатели через одну дробь. Заметим, что: 5x+3x+1=3x+3+2xx+1=3(x+1)+2xx+1=3+2xx+1the fraction with numerator 5 x plus 3 and denominator x plus 1 end-fraction equals the fraction with numerator 3 x plus 3 plus 2 x and denominator x plus 1 end-fraction equals the fraction with numerator 3 open paren x plus 1 close paren plus 2 x and denominator x plus 1 end-fraction equals 3 plus the fraction with numerator 2 x and denominator x plus 1 end-fraction Тогда исходное неравенство принимает вид: 2xx+123+2xx+1+822xx+12 raised to the the fraction with numerator x and denominator x plus 1 end-fraction power minus 2 raised to the 3 plus the fraction with numerator 2 x and denominator x plus 1 end-fraction power plus 8 is less than or equal to 2 raised to the the fraction with numerator 2 x and denominator x plus 1 end-fraction power Используя свойства степеней an+m=anama raised to the n plus m power equals a to the n-th power center dot a to the m-th power и a2n=(an)2a raised to the 2 n power equals open paren a to the n-th power close paren squared, перепишем уравнение: 2xx+18(2xx+1)2+8(2xx+1)22 raised to the the fraction with numerator x and denominator x plus 1 end-fraction power minus 8 center dot open paren 2 raised to the the fraction with numerator x and denominator x plus 1 end-fraction power close paren squared plus 8 is less than or equal to open paren 2 raised to the the fraction with numerator x and denominator x plus 1 end-fraction power close paren squared Шаг 2: Введение новой переменной Пусть t=2xx+1t equals 2 raised to the the fraction with numerator x and denominator x plus 1 end-fraction power , где t>0t is greater than 0. Подставим tt в неравенство: t8t2+8t2t minus 8 t squared plus 8 is less than or equal to t squaredПеренесем все члены в одну сторону: -9t2+t+80negative 9 t squared plus t plus 8 is less than or equal to 0Умножим на -1negative 1, меняя знак неравенства: 9t2t809 t squared minus t minus 8 is greater than or equal to 0Шаг 3: Решение квадратного неравенства Найдем корни уравнения 9t2t8=09 t squared minus t minus 8 equals 0 через дискриминант: D=(-1)249(-8)=1+288=289=172cap D equals open paren negative 1 close paren squared minus 4 center dot 9 center dot open paren negative 8 close paren equals 1 plus 288 equals 289 equals 17 squared t1=1+1718=1t sub 1 equals the fraction with numerator 1 plus 17 and denominator 18 end-fraction equals 1 t2=11718=89t sub 2 equals the fraction with numerator 1 minus 17 and denominator 18 end-fraction equals negative eight-nineths Так как ветви параболы направлены вверх, решением 9t2t809 t squared minus t minus 8 is greater than or equal to 0 является t(,-8/9][1,+)t is an element of open paren negative infinity comma negative 8 / 9 close bracket union open bracket 1 comma positive infinity close paren. Учитывая условие t>0t is greater than 0, получаем единственный промежуток: t1t is greater than or equal to 1. Шаг 4: Обратная подстановка Вернемся к переменной xx: 2xx+112 raised to the the fraction with numerator x and denominator x plus 1 end-fraction power is greater than or equal to 1 2xx+1202 raised to the the fraction with numerator x and denominator x plus 1 end-fraction power is greater than or equal to 2 to the 0 power Так как основание 2>12 is greater than 1, знак неравенства для показателей сохраняется: xx+10the fraction with numerator x and denominator x plus 1 end-fraction is greater than or equal to 0 Решим методом интервалов. Нуль числителя: x=0x equals 0. Нуль знаменателя: x=-1x equals negative 1. На интервалах (,-1)open paren negative infinity comma negative 1 close paren, (-1,0]open paren negative 1 comma 0 close bracket и [0,+)open bracket 0 comma positive infinity close paren выражение xx+1the fraction with numerator x and denominator x plus 1 end-fraction принимает знаки:

  1. На (,-1)open paren negative infinity comma negative 1 close paren: =+the fraction with numerator negative and denominator negative end-fraction equals positive (подходит) На (-1,0]open paren negative 1 comma 0 close bracket: +=the fraction with numerator negative and denominator positive end-fraction equals negative (не подходит) На [0,+)open bracket 0 comma positive infinity close paren: ++=+the fraction with numerator positive and denominator positive end-fraction equals positive (подходит)

Ответ: x \in (-\infty, -1) \cup [0, +\infty) Нужно ли вам графическое представление решения этого неравенства на числовой прямой?

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