Good for 15 seconds question! (Part 2)

Algebra Level 2

Let α \alpha and β \beta be the solutions of x 2 34 x + 34 = 0 x^2-34x+34=0 . What is the value of ( α + 1 ) ( β + 1 ) (\alpha+1)(\beta+1) ?


See part 1 here and part 3 here .


The answer is 69.

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4 solutions

f ( x ) = x 2 34 x + 34 = ( x α ) ( x β ) f(x) = x^2 - 34x + 34 = (x-\alpha)(x - \beta)

f ( 1 ) = 1 + 34 + 34 = ( 1 α ) ( 1 β ) f(-1) = 1 + 34 + 34 = (-1-\alpha)(-1 - \beta)

69 = ( 1 + α ) ( 1 + β ) \implies 69 = (1+\alpha)(1+\beta)

Therefore, answer is 69 \boxed{69}

pretty nice.

Jaymund Ostonal - 6 years, 4 months ago
Mj Santos
Feb 6, 2015

Note that: ( α + 1 ) ( β + 1 ) = α β + α + β + 1 (\alpha+1)(\beta+1)=\alpha\beta+\alpha+\beta+1

By Vieta's Identity we get the sum and products of the solutions of x 2 34 x + 34 x^2-34x+34 : a = 1 , b = 34 , c = 34 a=1, b=-34, c=34 α + β = b a = 34 \alpha+\beta=\frac{-b}{a}=34 α β = c a = 34 \alpha\beta=\frac{c}a=34

Substituting the value:

α β + α + β + 1 = 34 + 34 + 1 = 69 \alpha\beta+\alpha+\beta+1=34+34+1=\boxed{69}

Same method...

Mehul Arora - 6 years, 2 months ago

took more than 15 seconds.

U Z - 6 years, 4 months ago

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Well you should immediately think of the vieta's identity.

MJ Santos - 6 years, 4 months ago

Yes, I applied your method or you can say vieta method

Akash Papnai - 5 years, 9 months ago

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Same i did

Aman Dubey - 5 years, 4 months ago

(α+1)(β+1)=αβ+α+β+1 Now αβ=(c/a)=34 α+β=(-b/a)=34 hence, total is 69

Kumar Pranav
Feb 7, 2015

a+1*b+1=ab+a+b+1 Sum of roots =- b/a=34/1 Product of roots=c/a=34/1 Therefore, 34+34+1=69

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