A Cute Question From The Brazilian Math Olympiads

Algebra Level 1

Mary Ann entered the classroom and saw in the chalkboard some notes from the previous class, partially erased, as pictured. What is the coefficient of x x which has been erased from the top line of the chalkboard?

Note: Raízes in Portuguese is the Roots of the equations.
There is a negative sign in front of the coefficient. Your answer should be positive.

Image source: OBMEP 2005 (Brazilian Math Olympiads of Public Schools).


The answer is 22.

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15 solutions

Blesson Roy
Mar 31, 2014

since x=6 is given hence substituting this in the equation gives us 2(6*6) - A(6) + 60 =0. Hence A = wiped out number = 22

correct ans is 22..

zarree khan - 7 years, 2 months ago

lol it is so easy

Uttam Bhadauriya - 7 years, 2 months ago

22

Chaurasiya Ana - 7 years, 1 month ago

Set the erased number as y and x =6: 72 - 6y + 60 = 0 ; y = ( 72 + 60 ) / 6 ; y = 22

Murali K S
Apr 10, 2014

We must use the concept of producr of roots tat is c/a and sum of roots tat is -b/a

But the another root is unknown to us, then how can we use the procedure of sum or product of the roots...???

Shreyans Badjatay - 7 years, 1 month ago

Set the unknown coefficient as a then plug in the value of 6 for x and then solve: 2 ( 6 2 ) a ( 6 ) + 60 = 0 2(6^2)-a(6)+60=0 72 6 a + 60 = 0 72-6a+60=0 6 a = 72 + 60 6a=72+60 a = 132 6 a=\frac{132}{6} a = 22 a=22

the first solution is x=6, the seconde must be x=5 to have 2 6 5=60 2(x-6)(x-5)=2( x²-5x-6x+30)=2x²-22x-60

Mudra Desai
Apr 1, 2014

2(6^2)-6y+60=0 so 6y=132 and y=22

Nikko Quirap
Apr 11, 2014

let C be the value of the coefficient of x then substitute the value of x=6 6C=2(6*6)+60 C=22

Allen Alexander
Apr 10, 2014

take the coefficient to be k and substitute x=6 so we obtain 72-k6+60=0 or 132-k6=0 or k6=132 or k=132/6 = 22

Arthur Paderan
Apr 8, 2014

Just represent the coefficient of x with any variable then substitute all x's with 6, then simplify to get 22.

Diasdo Siadari
Apr 8, 2014

In the chalkboard we can see that one of the root of the equation is 6. So, we can subtitute one of the root to get the answer, 2(6*6)-a(6)+60=0.--> 72+60=6a.--> a=22. Finish.

By letting 2x^2 - ax + 60 = 0,

as one of the 2 roots is 6,

2(6)^2 - 6a + 60 = 0 ,

72 + 60 = 6a

a = 132 / 6 = 22,

therefore a=22 ,would be 2x^2 - 22x + 60,

For x = 6 then the initial equation that is 2x ^ 2-ax +60 = 2 (6) ^ 2-a (6) +60=72-6a +60= 132-6a = 0 so obtained a = (-132) / (-6) = 22

22

Aswad Hariri Mangalaeng - 7 years, 2 months ago

let the product value is 120. so we can solve it by (12*10)=120. hence the sum of (12 and 10) will be the answer.

Afzal Sajid
Apr 4, 2014

2(6*6) - 6y+60=0 so 6y =132 and y=22

Root X = 6; (x-6) , (2x-n); x=n/2, then 6n = 60

the product of the roots is c/a; hence, 60/2=6*x; where x is another root, so, another root is 5; the sum of the root is -b/a; hence, -(-coefficient)/2=6+5; hence, coefficient =22

Abhijeet Rathore - 7 years, 2 months ago

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