Evaluate (x – 2y – z)2

(i) (x – 2y – z)2

(ii) (2x – 3y + 4z)2

Answer :

(i) (x – 2y – z)2

It can be written as

= [x + (-2y) + (-z)]2

By further calculation

= (x)2 + (-2y)2 + (-z)2 + 2 × x × (-2y) + 2 × (-2y) × (-z) + 2 × (-z) × x

So we get

= x2 + 4y2 + z2 – 4xy + 4yz – 2zx

(ii) (2x – 3y + 4z)2

It can be written as

= [2x + (-3y) + 4z]2

By further calculation

= (2x)2 + (-3y)2 + (4z)2 + 2 × 2x × (-3y) + 2 × (-3y) × 4z + 2 × 4z × 2x

So we get

= 4x2 + 9y2 + 16z2 -12xy – 24yz + 16zx

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