Question 20Factorised form of r2−10r+21 isa r−1r−4b r−7

Question 20Factorised form of r2−10r+21 isa r−1r−4b r−7
| Question 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)
 

Please scroll down to see the correct answer and solution guide.

Right Answer is:

SOLUTION

b) (r−7)(r−3)

We have,
​​​​​​​ r2−10r+21=r2−7r−3r+21=r(r−7)−3(r−7)
[by spliting the middle term, so that product of their numerical coefficients is equal constant term]
=(r−7)(r−3)          [∵ x2+(a+b)x+ab=(x+a)(x+b)]

Related Questions