The equation 2 x 2 − 6 2 x + k = 0 has two real roots, one of which is 1 more than twice the other. Find the value of k .
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correct
let the first root be "t" then by given condition the second root is "2t+1" now, sum of roots= t+2t+1 = -b/a = 62/2 so that t=10 product of roots t*(2t+1)= c/a = k/2 by putting value of t , k=420
let roots are x, 2x+1. 31=x+2x+1 x=10 K/2=10*21 k=420
I started by trying to simplify the equation. Dividing both sides by two, the equation becomes:
x 2 − 3 1 x + 2 k = 0
By simple factoring (given that the answers are both real integers), we come up with the equation:
( x − [ k + 1 ] ) ( x − 2 k ) = 0
Using the FOIL method, we can then presume that:
2 − k x + − ( k + 1 ) x = − 3 1 x
This gives us:
2 k x − k x − x = − 3 1 x
Factoring x out of both sides, we get:
2 k + k + 1 = 3 1
2 3 k = 3 0 , and we get k = 20.
If k = 20, then we can presume that one of the roots is 10. The other root would then be 21, fulfilling the problem requirements.
21 x 10 = 210, but because we divided the equation at the very beginning by 2, the value of k would be:
2 1 x 1 0 x 2 = 4 2 0
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Let one of the roots be α
and let the other root be 2 α + 1
from the equation given, a = 2 b = − 6 2
and c = k
sum of the roots equals α + 2 α + 1 = a − b = 2 6 2
3 α + 1 = 3 1
α = 1 0
product of the roots equals α ( 2 α + 1 ) = a c = 2 k
2 ( α ) 2 + α = 2 k
k = 4 ( α ) 2 + 2 α
but α = 1 0
thus, k = 4 ( 1 0 ) 2 + 2 ( 1 0 )
k = 4 0 0 + 2 0
Hence k = 4 2 0
x1+x2= -b/a
x1 *x2= c/a
x1+2*(x2) +1 = -(-62)/2>>>>x1=10
x2=2*x2 +1>>>>> X2=21
10 *21= K/2
K= 420
two real roots m,n m+n= - (-62)/2 =31, m=2n+1, 2n+1+n=31, n=10, m=21,
product of two roots =m n =21 10=210=k/2, k=420.
Did you use Vietta's Theorem?
what lesson is this ????
the equation has 2 real roots which are x1 and x2 a=2 b=-62 c=k
x2=2x1+1
x1+x2=x1+2x1+1=-b/a=62/2=31
x1=10
x1 x2=x1 (2x1+1)=210=c/a=k/2
therefore k=210*2 =420
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Let the roots be r and 2r+1 ( x − r ) ( x − 2 r − 1 ) = 0 = > x 2 − ( 3 m + 1 ) x + 2 m 2 + m = 0 From the equation, comparing coefficients of x we get = > 3 m + 1 = 6 2 / 2 = 3 1 i.e. m = 1 0 and comparing coefficients of last term we get k / 2 = 2 m 2 + m = 2 1 0 = > k = 4 2 0