If x=-1 , what is the value of 2x²+x
Answers
Answer:
Consider a quadratic polynomial in x f(x)=ax
2
+bx+c
Differentiating f(x) with respect to
dx
df(x)
=
dx
d(ax
2
+bx+c)
=2ax+b=0 (for maxima minima)
x=
2a
−b
...(i)
Double differentiating f(x) with respect to x
dx
2
d
2
f(x)
=
dx
2
d
2
(ax
2
+bx+c)
=2a ...(ii)
dx
2
d
2
f(x)
>0 for minimum and
dx
2
d
2
f(x)
<0 for maximum
Therefore if 2a<0 then the polynomial has a maximum at x=
2a
−b
and if 2a>0 then the polynomial has a minimum at x=
2a
−b
Consider the given polynomial 2x
2
+x−1
a=2, b=1,c=-1
Hence a>0, so at x=
2a
−b
the given polynomial will have a minimum from i and ii
2a
−b
=
4
−1
Substituting in the quadratic polynomial we get
2(
16
1
)−
4
1
−1
=
8
1−2−8
=
8
−9
Hence the answer is C
Answer:
-1 is the answer.
As you have to put -1 in the place of x and then solve
