**Resolution of Vector in Three Dimensional Co-ordinates**

While expressing a vector quantity with its components we will consider resolution only in three dimensional rectangular coordinates.

In three dimensional coordinate system a position vector can be expressed in the following way.

ř = î x + ĵ y + ƙ z. Here position coordinate of P is (x, y, z).

**Proof:** Let OX, OY and OZ be three lines perpendicular to one another and corresponds to X, Y and Z axes respectively [Figure].

Let a position vector ř be represented by line OP, in this axes-system, both in magnitude and direction.

Let consider that the co-ordinate of P is (x, y, z) and î, ĵ and ƙ are the unit vectors along the axes X, Y and Z respectively. Here PR is drawn normal to plane XY and RQ is normal to OX [Figure].

Now, from figure,

OP = OR + RP and

OR = OQ + QR

so, OP = OQ + QR + RP

but, OQ = x î . QR = y ĵ . RP = z ƙ

and, OP = ř

So, ř = x î + y ĵ + z ƙ

Here, x, y and z are the components of vector ř along X, Y and Z axis respectively.

**Modulus of ř:**

From figure we get,

OP^{2} = OR^{2} + RP^{2} and, OR^{2} = OQ^{2} + QR^{2}

so, OP^{2} = OQ^{2} + QR^{2} + RP^{2}

or, r^{2} = x^{2} + y^{2} + z^{2}

then, r = √( x^{2} + y^{2} + z^{2})