Choose the expression that is equivalent to [tex]\left(7^{-2} \cdot 7^3\right)^{-3}[/tex].

A. [tex]-76[/tex]

B. [tex]\frac{1}{7^3}[/tex]

C. [tex]-\frac{1}{7^6}[/tex]

D. [tex]7^{18}[/tex]



Answer :

To solve the expression [tex]\(\left(7^{-2} \cdot 7^3\right)^{-3}\)[/tex], we need to follow the laws of exponents step-by-step.

1. Simplify the expression inside the parentheses:
[tex]\[ 7^{-2} \cdot 7^3 \][/tex]
When multiplying terms with the same base, we add the exponents:
[tex]\[ 7^{-2 + 3} = 7^1 = 7 \][/tex]

2. Raise the simplified result to the power of -3:
[tex]\[ (7^1)^{-3} \][/tex]
When raising a power to another power, we multiply the exponents:
[tex]\[ 7^{1 \cdot -3} = 7^{-3} \][/tex]

3. Rewrite the expression with a positive exponent:
[tex]\[ 7^{-3} = \frac{1}{7^3} \][/tex]

Comparing this to the given choices:
- [tex]\( -76 \)[/tex]
- [tex]\(\frac{1}{7^3}\)[/tex]
- [tex]\(-\frac{1}{7^6}\)[/tex]
- [tex]\(7^{18}\)[/tex]

The correct equivalent expression is [tex]\(\frac{1}{7^3}\)[/tex].

Thus, the correct answer is:
[tex]\[ \boxed{\frac{1}{7^3}} \][/tex]