Let's substitute the values of \( a = 2 \) and \( b = 9 \) into the expression \( 2a^2 - \frac{1}{3b} \).

Given:
\[
2a^2 - \frac{1}{3b}
\]

Substituting the values:
\[
2(2)^2 - \frac{1}{3(9)}
\]

Simplify:
1. Calculate \( 2^2 \):
\[
2^2 = 4
\]
2. Multiply by 2:
\[
2 \times 4 = 8
\]
3. Calculate \( 3 \times 9 \):
\[
3 \times 9 = 27
\]
4. Calculate \( \frac{1}{27} \):
\[
\frac{1}{27} \approx 0.037
\]

Final expression:
\[
8 - 0.037 \approx 7.963
\]

So, the value of the expression is approximately \( 7.963 \).

Would you like further details or have any questions? Here are some related questions:

1. How do you simplify expressions with fractions?
2. What happens when you change the values of \( a \) and \( b \)?
3. Can you solve similar expressions involving roots or powers?
4. How can we round decimals to different places?
5. How do expressions with variables behave in equations?

**Tip:** Always simplify inside the parentheses first when substituting values into an expression.

Learn how to solve the expression 2a² - 1/3b by substituting a=2 and b=9. This step-by-step solution involves key algebraic concepts such as substitution, exponents, and simplifying fractions. Suitable for students in Grades 6-8.

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