Maths help request

[K.I.L.E.R]

Today I'm going to ask my teacher why haven't we learned quaternions.

Second of all I want you guys to check if I'm converting a quaternion to an Euler angle properly.

Scalar scalar = null;
        final double sinSqr;
        final double cos;
        final double sin;
        
        scalar = v.getDirection();
        sinSqr = Math.sin(angle / 2) * Math.sin(angle / 2);
        cos = Math.cos(angle / 2);
        sin = Math.sin(angle / 2);
        
        matrix[0] *= 1 - 2 * sinSqr * (scalar.y * scalar.y + scalar.z * scalar.z);
        matrix[1] *= (2 * sinSqr * scalar.x * scalar.y) - (2 * cos * sin * scalar.z);
        matrix[2] *= (2 * sinSqr * scalar.x * scalar.z) + (2 * cos * sin * scalar.y);
        
        matrix[4] *= 2 * sinSqr * scalar.x * scalar.y + 2*cos * sin * scalar.z;
        matrix[5] *= 1 - 2 * sinSqr * (scalar.x * scalar.x + scalar.z * scalar.z);
        matrix[6] *= (2 * sinSqr * scalar.y * scalar.z) - (2 * cos * sin * angle);
        
        matrix[8] *= 2 * sinSqr * scalar.x * scalar.z - 2*cos * sin * scalar.y;
        matrix[9] *= (2 * sinSqr * scalar.y * scalar.z) + (2 * cos * sin * scalar.x);
        matrix[10] *= 1 - 2 * sinSqr * (scalar.x * scalar.x + scalar.y * scalar.y);

Thanks.