Which of the following numbers is in standard form?
- A$21.56 × 10^5$
- B$215.6 × 10^4$
- ✓$2.156 × 10^6$
- DNone of these.
Let option $(a)$ $\frac{2^{3}\times3^{3}}{4\times18}=\frac{2\times2\times2\times3\times3}{4\times18}$
$=\frac{4\times18}{4\times18}=1$
For option $(b)$, $[(-2)^{3}\times(-2)^{4}]\div(-2)^{7}=\frac{(-2)^{3}\times(-2)^{}4}{(-2)^{7}}$
$=\frac{(-2)^{3+4}}{(-2)^{7}}$ $\big[\because\text{a}^{\text{m}}\times\text{a}^{\text{n}}=\text{a}^{\text{m+n}}\big]$
$=\frac{(-2)^{7}}{(-2)^{7}}=1$ $\big[\because\frac{\text{a}^{\text{m}}}{\text{a}^{n}}=\text{a}^{\text{m-n}}\big]$
For option $(c)$, $=\frac{3^{0}\times5^{3}}{5\times25}=\frac{1\times5\times5\times5}{5\times25}$
$=\frac{5\times25}{5\times25}=1$ $\big[\because\text{a}^{0}=1\big]$
For option $(d)$, $\frac{2^{4}}{(7^{0}+3^{0})^{3}}=\frac{2^{4}}{(1+1)^{3}}$ $\big[\because\text{a}^{0}=1\big]$
$=\frac{2^{4}}{2^{3}}=2^{4-3}$ $\big[\because\frac{\text{a}^{m}}{\text{a}^{\text{n}}}=\text{a}^{\text{m-n}},\text{m>n}\big]$
$=-2^{1}=2$
Hence, option $(d)$ is not equal to $1$.
$4^{2\text{x}}=\frac{1}{32}$
$\Rightarrow(2^2)^{2\text{x}}=\frac{1}{2^5}$
$\Rightarrow2^{4\text{x}}2^{-5}$
$\Rightarrow4\text{x}=-5$
$\text{x}=\frac{-5}{4}$
$\because\Big(\frac{5}{6}\Big)^0=1$ $\bigg\{\because\Big(\frac{\text{a}}{\text{b}}\Big)^0=1\bigg\}$
Since,
$\Big\{(33)^2-(31)^2\Big\}^{\frac{5}{7}}$
$=\{1089-961\}^{\frac{5}{7}}$
$=\{128\}^{\frac{5}{7}}$
$=\{2^7\}^{\frac{5}{7}}$
$=2^{7\times\frac{5}{7}}$$[\text{As, }(\text{x}^{\text{m}})^{\text{n}}=\text{x}^{\text{mn}}]$
$=2^5$
$=32$
Hence, the correct alternative is option $(c)$.