Square of 9x - 7xy is
(a) 81x² + 49x²y²
(b) 81x² - 49x²y²
(c) 81x² + 49x²y² - 126x²y
(d) 81x² + 49x²y² - 63x²y

Solution:

Correct option is (c ).

Given, Square of 9x - 7xy = (9x - 7xy)²

Using the identity, (a - b)² = a² - 2ab + b²

Here a = 9x and b = 7xy

∴ (9x - 7xy)² = (9x)² - (2 × 9x × 7xy) + (7xy)²

= 81x² - 126x²y + 49x²y²

✦ Try This: Square of (3p + 2q) is (a) 9p² + 4q², (b)9p² - 4q², (c) 9p² + 12pq + 4q², (d) 9p² - 12pq + 4q²

Correct option is (c)

(3p + 2q)² , by using the identity, (a + b)² = a² + b² + 2ab

Here, a = 3p and b = 2q

Substituting in the formula we get

(3p + 2q)² = (3p)² + 2(3p)(2q) + (2q)²

= 9p² + 12pq+ 4q²

☛ Also Check: NCERT Solutions for Class 8 Maths Chapter 9

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NCERT Exemplar Class 8 Maths Chapter 7 Problem 18

Square of 9x - 7xy is (a) 81x² + 49x²y², (b) 81x² - 49x²y², (c) 81x² + 49x²y² - 126x²y, (d) 81x² + 49x²y² - 63x²y

Summary:

Square of 9x - 7xy is 81x² - 126x²y + 49x²y²

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