English

Multiply x2 + 4y2 + z2 + 2xy + xz – 2yz by (–z + x – 2y).

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Question

Multiply x2 + 4y2 + z2 + 2xy + xz – 2yz by (–z + x – 2y).

Sum
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Solution

According to the question:

(x2 + 4y2 + z2 + 2xy + xz – 2yz) × (–z + x – 2y)

Now, multiply as follows:

= {x + (–2y) + (–z)}{(x)2 + (–2y)2 + (–z2) – (x)(–2y) – (–2y)(–z) – (–z)(x)}

= x3 + (–2y)3 + (–z)3 – 3 × x × (–2y) × (–z)

Use the identity:

(a + b + c)(a2 + b2 + c2 – ab – bc – ca) = a3 + b3 + c3 – 3abc

= x3 – 8y3 – z3 – 6xyz

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Chapter 2: Polynomials - Exercise 2.4 [Page 23]

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NCERT Exemplar Mathematics Exemplar [English] Class 9
Chapter 2 Polynomials
Exercise 2.4 | Q 6. | Page 23

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