Q.

Find a quadratic polynomial whose zeroes are 4   and 3   .


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a

x 2 7x+12  

b

5 x 2 +9x+1  

c

3 x 2 +5x+10   

d

2 x 2 6x+12  

answer is B.

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Detailed Solution

Given that 4   and 3   are zeroes of a quadratic polynomial. We need to form a quadratic polynomial.
When α   and β   are the zeroes of quadratic polynomial, the two equations formed with zeroes are given as:
α + β  =  b a   and αβ =  c a    where b   is the coefficient of linear term, c   is constant while a   is the coefficient of quadratic term in quadratic polynomial.
Based on the relationship between zeroes and polynomials we have quadratic polynomial as:
f(x)= x 2 (α+β)x+αβ...(i)   where α&β   are the zeroes of the polynomial.
Now we have,
Sum of zeroes,
α + β  = 4+3 α + β  = 7  
and
Product of zeroes,
  αβ = 4×3 αβ = 12  
Now equating the value of α+β   and αβ   in equation (i)  , we have,
f(x)= x 2 7x+12  
Hence, the value of the quadratic polynomial is x 2 7x+12  .
Therefore, option 2 is correct.
 
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