How To Solve These? Factoring 1. X^2-10x+21= 2. 9x^2-25= 3. X62+10x+25=


5 Answers

Oddman Profile
Oddman answered
X2-10x+21 = (x-3)(x-7)

9x2-25 = (3x+5)(3x-5)

x2+10x+25 = (x+5)2
It is helpful to know your multiplication tables, so you can find factors that meed certain criteria.
In the first problem, you are looking for factors of 21 that add to 10. The numbers that divide 21 are (1, 21) or (3, 7). Of these, the latter pair add to 10.

The second problem is a standard form: The difference of 2 squares.

The third problem seeks factors of 25 that add to 10. You know they're not 1 and 25, so 5 and 5 is the other (useful) choice.

Emilia Singletary Profile
D=b^2-4ac=100-4*21=16, x1=(10+4)/2=7,x2=(10-4)/2=3 factoring (x-7)(x-3)
x^2=25/9, x1=+5/3, x2=-5/3, factoring (x-5/3)(x+5/3), or (3x-9)(3x+9)
did you mean x^2+10x+25, if so you have: Same discriminant as 1., but the roots will be x1=(-10+4)/2 and (-10-4)/2, factoring (x+3)(x+7)
Anonymous Profile
Anonymous answered
Anonymous Profile
Anonymous answered
X ^2 + 10X + 21

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