# NCERT Class 12-Mathematics: Exemplar Chapter –4 Determinants Part 10

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**Question 19:**

Using matrix method, solve the system of equations , and .

**Answer:**

Given system of equation is

In the form of

For

Now,

**Question 20:**

Given , find BA and use this to solve the system of equations .

**Answer:**

We have,

Also,

**Question 21:**

If and , then prove that *.*

**Answer:**

Let

Applying , we get

Taking common from the first column, we get

Now, Expanding along , we get

Given that

But it is given that

Hence Proved