Factorised form of r² - 10r + 21 is
(a) (r - 1) (r - 4)
(b) (r - 7) (r - 3)
(c) (r - 7) (r + 3)
(d) (r + 7) (r + 3)

Solution:

Correct option is (b).

Given, r² - 10r + 21

On factoring this polynomial, we get

= r² - 7r - 3r + 21

= r(r - 7) - 3(r - 7)

= (r - 3) (r - 7)

✦ Try This: Factorisred form of x² + 3x - 18 is (a) (x + 6)(x - 3), (b) (x + 6)(x + 3), (c) (x - 6)(x - 3), (d) (x - 6)(x +3)

Correct option is (a)

Given, x² + 3x - 18

= x² - 3x + 6x - 18

= x( x - 3) + 6( x - 3)

=(x + 6)(x - 3)

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

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NCERT Exemplar Class 8 Maths Chapter 7 Problem 20

Factorised form of r² - 10r + 21 is (a) (r - 1) (r - 4) (b) (r - 7) (r - 3) (c) (r - 7) (r + 3) (d) (r + 7) (r + 3)

Summary:

Factorised form of r² - 10r + 21 is (r - 3) (r - 7)

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