Assertion : A vector `vecA` can be resolved into component along with given vectors `veca and vecb` lying in the same plane.
Reason : `vecA = lambda veca + mu vecb` where `lambda` and `mu` are real numbers.

Answer

To solve the question, we need to analyze the assertion and the reason given:

**Assertion:** A vector \(\vec{A}\) can be resolved into components along given vectors \(\vec{a}\) and \(\vec{b}\) lying in the same plane.

**Reason:** \(\vec{A} = \lambda \vec{a} + \mu \vec{b}\) where \(\lambda\) and \(\mu\) are real numbers.

### Step-by-Step Solution:

1. **Understanding Vector Resolution**:
- A vector can be resolved into components along other vectors if those vectors lie in the same plane. This means that any vector in that plane can be expressed as a combination of the two vectors.

**Hint:** Recall that any vector in a plane can be expressed as a linear combination of two non-parallel vectors in that plane.

2. **Identifying Coplanarity**:
- The vectors \(\vec{a}\) and \(\vec{b}\) are said to be coplanar with \(\vec{A}\). For three vectors to be coplanar, one vector must be expressible as a linear combination of the other two.

**Hint:** Remember the definition of coplanarity: three vectors are coplanar if one can be expressed as a combination of the others.

3. **Linear Combination**:
- The expression \(\vec{A} = \lambda \vec{a} + \mu \vec{b}\) indicates that \(\vec{A}\) can be written as a combination of the vectors \(\vec{a}\) and \(\vec{b}\) with real coefficients \(\lambda\) and \(\mu\). This confirms that \(\vec{A}\) can indeed be resolved into components along \(\vec{a}\) and \(\vec{b}\).

**Hint:** A linear combination involves multiplying each vector by a scalar and adding the results.

4. **Conclusion**:
- Since both the assertion and the reason are true, and the reason provides a valid explanation for the assertion, we conclude that both the assertion and reason are correct.

**Hint:** When evaluating assertions and reasons, check if the reason logically supports the assertion.

### Final Answer:
Both the assertion and the reason are true, and the reason explains the assertion.