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Algebra Level 4

(x+2). (x+3). (x-4). (x-5) = 44 If a,b,c,d are the roots of the equations above then find the value of: a+b+c+d+ abcd


The answer is 80.

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4 solutions

Rick B
Jan 20, 2015

Let's analyze the equation ( x + 2 ) ( x + 3 ) ( x 4 ) ( x 5 ) = 0 (x+2)(x+3)(x-4)(x-5) = 0

The sum of its roots is the same as that of the equation of the problem, because subtracting 44 44 from the product doesn't change the coefficient of x 3 x^3 , which is equal to 2 + 3 4 5 = 4 2+3-4-5 = -4 , giving a + b + c + d = 4 a+b+c+d = 4

And the product of the roots of the equation above is 2 × 3 × 4 × 5 = 120 2 \times 3 \times 4 \times 5 = 120 (I ignored the negative signs because there is an even amount of them). But a b c d = 120 44 = 76 abcd = 120-44 = 76

So a + b + c + d + a b c d = 4 + 76 = 80 a+b+c+d+abcd = 4+76 = \boxed{80}

Yupp did the same way

Rajat Bisht - 6 years, 4 months ago

Hey, Question is (x+2)(x+3)(x-4)(x-5)=44 not equal to 0

Viswa Prasad - 6 years, 3 months ago

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I know, I just used the one that's equal to 0 0 because it shares some similarities with the one of the problem.

Rick B - 6 years, 2 months ago

We take 44 on the LHS so the RHS=0.

As mention coefficient of x^3 remains the same and is equal to the sum of constants of each parenthesis..

Niranjan Khanderia - 3 years, 2 months ago

Used the same logic.

Niranjan Khanderia - 3 years, 2 months ago
Ting Sie Kim
Jan 14, 2015

absolutely right , i expected this type of solution only, i also used the same method to some extent .

Parv Maurya - 6 years, 5 months ago
Ankit Kumar Jain
Feb 6, 2015

Solve the equation and you get x 4 4 x 3 + 19 x 2 + 46 x + 76 x^{4} - 4x^{3} + 19x^{2} + 46x + 76 .

Now by Vieta's Theorem Sum of Roots = 4 and Product of roots = 76.

Therefore 80 \boxed{80}

Jyotsna Sharma
Jan 7, 2015

(x+2)(x+3)(x-4)(x-5)=44 when expanded, can be written as x^4-4x^3-19x^2+46x+76=0 sum of roots = -(-4)/1=4 product of roots = 76/1 (a+b+c+d)+abcd=4+76=80

nice solution , can be used though but if the question was edited and made a bit complex , then one would have to find value of all the roots then solve it.

Parv Maurya - 6 years, 5 months ago

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It depends on what is asked . For instance here it was directly asked something related to sum of roots and product of roots , so we could use this concept. Please also mention the method used by you to solve the same.

Jyotsna Sharma - 6 years, 5 months ago

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i'll post my method in a couple of days or so

Parv Maurya - 6 years, 5 months ago

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