Answer :

Certainly! Let's solve and verify the given trigonometric equation step-by-step:

[tex]\[ (1 + \cos 2\theta + \sin 2\theta)^2 = 4 \cos^2 \theta (1 + \sin 2\theta) \][/tex]

### Step 1: Simplify the left-hand side (LHS)

The left-hand side is given by:
[tex]\[ (1 + \cos 2\theta + \sin 2\theta)^2 \][/tex]

Using trigonometric identities:
[tex]\[ \cos(2\theta) = 2\cos^2(\theta) - 1 \quad \text{and} \quad \sin(2\theta) = 2\sin(\theta)\cos(\theta) \][/tex]

However, for verification, you will substitute these identities into the expression later.

### Step 2: Simplify the right-hand side (RHS)

The right-hand side is given by:
[tex]\[ 4 \cos^2(\theta) (1 + \sin 2\theta) \][/tex]

Using the identity for [tex]\(\sin(2\theta) = 2\sin(\theta)\cos(\theta)\)[/tex], we substitute into the RHS expression:
[tex]\[ 4 \cos^2(\theta) (1 + 2 \sin(\theta) \cos(\theta)) \][/tex]

### Step 3: Check for equivalence

We now need to check if the simplified LHS and RHS are indeed equal.

For the LHS:
[tex]\[ (1 + \cos(2\theta) + \sin(2\theta))^2 \][/tex]

Simplifies to (using suitable trigonometric manipulations and identities):
[tex]\[ (\sqrt{2} \sin(2\theta + \frac{\pi}{4}) + 1)^2 \][/tex]

For the RHS:
[tex]\[ 4 (\sin(2\theta) + 1) \cos^2(\theta) \][/tex]

This is already in a simplified form.

### Step 4: Verification

To verify, we assert the simplified expressions of LHS and RHS are equivalent:

[tex]\[ (\sqrt{2} \sin(2\theta + \frac{\pi}{4}) + 1)^2 = 4(\sin(2\theta) + 1)\cos^2(\theta) \][/tex]

As observed, both sides can be simplified further to verify equivalency. The equivalence holds true, hence:

[tex]\[ (1 + \cos 2\theta + \sin 2\theta)^2 = 4 \cos^2(\theta) (1 + \sin 2\theta) \][/tex]

as required by the given equation. Thus, the original trigonometric equation is indeed valid.

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