01Математика - 9 класс. Алгебра - Степень с рациональным показателем в виде десятичной дроби

Задание

Найдите значение выражения \(\displaystyle 16^{-0{,}{75}}\small.\)

Таблица степеней

Информация

Таблица степеней

		С т е п е н и
		\(\displaystyle \bf \color{blue}{2}\)	\(\displaystyle \bf \color{blue}{3}\)	\(\displaystyle \bf \color{blue}{4}\)	\(\displaystyle \bf \color{blue}{5}\)	\(\displaystyle \bf \color{blue}{6}\)	\(\displaystyle \bf \color{blue}{7}\)	\(\displaystyle \bf \color{blue}{8}\)
Ч и с л а	\(\displaystyle \bf \color{blue}{2}\)	\(\displaystyle 4\)	\(\displaystyle 8\)	\(\displaystyle 16\)	\(\displaystyle 32\)	\(\displaystyle 64\)	\(\displaystyle 128\)	\(\displaystyle 256\)
	\(\displaystyle \bf \color{blue}{3}\)	\(\displaystyle 9\)	\(\displaystyle 27\)	\(\displaystyle 81\)	\(\displaystyle 243\)	\(\displaystyle 729\)	\(\displaystyle 2187\)	\(\displaystyle 6561\)
	\(\displaystyle \bf \color{blue}{4}\)	\(\displaystyle 16\)	\(\displaystyle 64\)	\(\displaystyle 256\)	\(\displaystyle 1024\)	\(\displaystyle 4096\)	\(\displaystyle 16384\)	\(\displaystyle \ldots\)
	\(\displaystyle \bf \color{blue}{5}\)	\(\displaystyle 25\)	\(\displaystyle 125\)	\(\displaystyle 625\)	\(\displaystyle 3125\)	\(\displaystyle 15625\)	\(\displaystyle \ldots\)	\(\displaystyle \ldots\)
	\(\displaystyle \bf \color{blue}{6}\)	\(\displaystyle 36\)	\(\displaystyle 216\)	\(\displaystyle 1296\)	\(\displaystyle 7776\)	\(\displaystyle \ldots\)	\(\displaystyle \ldots\)	\(\displaystyle \ldots\)
	\(\displaystyle \bf \color{blue}{7}\)	\(\displaystyle 49\)	\(\displaystyle 343\)	\(\displaystyle 2401\)	\(\displaystyle 16807\)	\(\displaystyle \ldots\)	\(\displaystyle \ldots\)	\(\displaystyle \ldots\)
	\(\displaystyle \bf \color{blue}{8}\)	\(\displaystyle 64\)	\(\displaystyle 512\)	\(\displaystyle 4096\)	\(\displaystyle 32768\)	\(\displaystyle \ldots\)	\(\displaystyle \ldots\)	\(\displaystyle \ldots\)
	\(\displaystyle \bf \color{blue}{9}\)	\(\displaystyle 81\)	\(\displaystyle 729\)	\(\displaystyle 6561\)	\(\displaystyle 59049\)	\(\displaystyle \ldots\)	\(\displaystyle \ldots\)	\(\displaystyle \ldots\)
	\(\displaystyle \bf \color{blue}{10}\)	\(\displaystyle 100\)	\(\displaystyle 1000\)	\(\displaystyle 10000\)	\(\displaystyle 100000\)	\(\displaystyle \ldots\)	\(\displaystyle \ldots\)	\(\displaystyle \ldots\)

Решение

Представим показатель в виде обыкновенной дроби:

\(\displaystyle {-0{,}{75}}=-\frac{3}{4}\small.\)

Запишем данное выражение в виде

\(\displaystyle 16^{-0{,}{75}}=16^{-\frac{3}{4}}=16^{\frac{-3}{4}}\small.\)

Используем

Определение

Определение степени с рациональным показателем

Если \(\displaystyle a>0\) и \(\displaystyle \frac{m}{n}\)– рациональное число, где \(\displaystyle m\)– целое, а \(\displaystyle n\)– натуральное, то

\(\displaystyle a^{\frac{m}{n}}=\sqrt[n]{a^m}\small.\)

при \(\displaystyle a=16\small,\) \(\displaystyle m=-3\) и \(\displaystyle n=4\small.\)

Получим

\(\displaystyle 16^{\frac{\color{blue}{-3}}{\color{red}{4}}}=\sqrt[{\color{red}{4}}]{16^\color{blue}{-3}}=(\sqrt[4]{{16}})^{-3}=2^{-3}=\frac{1}{8}=0{,}125\small.\)

Ответ: \(\displaystyle 0{,}125\small.\)

Теория: 03 Степень с рациональным показателем в виде десятичной дроби

Таблица степеней

С т е п е н и

Ч и с л а

Определение степени с рациональным показателем

Ч
и
с
л
а