Q. 5 C4.2( 5 Votes )

Factories the following expressions

p2 – 10p + 21

Answer :

The given expression looks as


x2 + (a + b)x + ab


where a + b = -10; and ab = 21;


factors of 21 their sum


-1 × -21 -1-18 = -19


-7 × -3 -7-3 = -10


the factors having sum -10 are -7 and -3


p2 + 9p + 18 = p2 + (-7-3)p + 21


= p2 -7p-3p + 21


= p(p-7) -3(p-7)


= (p-7)(p-3)


Hence the factors of p2 + 9p + 18 are (p-7) and (p-3)


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