Question

1) Factors of the given expression (x2- 4xy - 221) are....​

Answer 1

Answer:

∴x2−4x−21=(x−7)(x+3)

Step-by-step explanation:

Because the quadratic x

(2−4) x−21

has 1

as its coefficient of x

2

we will start with two brackets like this:

(x±a)(x±b)

what is left to be determined are the values for

a&b

to decide what these numbers are we look for two numbers that multiply to give the constant

ie.−21

but add up to the coefficient of x

ie.−4

this we do by inspection, taking note of the signs

a=1

,b=−21

sum=1−21=20

incorrect

a=−3

,b=7

sum=4

correct value but incorrect sign

a=3

b=−7

sum=−4

correct value and sign

∴x2−4x−21=(x−7)(x+3)