Match List I with List II
| LIST I | LIST II | ||
| A. |
The maximum value if the function $f(x)=25x-\frac{5x^2}{2}+7$ in $[-1, 6]$ is |
I. | 24 |
| B. |
The minimum value of the function $f(x)=2x^3-15x^2+36x+1$ in [1, 5] is |
II. | $\frac{1}{16}$ |
| C. |
The maximum value of the function $f(x)=\frac{x}{2}-x^2$ in [0, 1] is |
III. | $\frac{139}{2}$ |
| D. |
The least value of the function $f(x)=\frac{9}{(x+3)}+x$ in [-7, 1]. x ≠ -3 is |
IV. | $-\frac{37}{4}$ |
Choose the correct answer from the options given below :
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A-III, B-I, C-II, D-IV
(A) $f(x)=25x-\frac{5x^2}{2}+7$
for max. value, $f'(c)=0$
$⇒25-5x=0$
$⇒x=5$
$f(5)=125-\frac{125}{2}+7=\frac{139}{2}$
(B) $f(x)=2x^3-15x^2+36x+1$
for min. value $f'(c)=0$
$⇒f'(c)=6x^2-30x+36=0$
$⇒x^2-5x+6=0$
$⇒(x-3)(x-2)=0$
$x=3\,or\,2$
$⇒f''(c)>0⇒2x-5>0$
for $f''(3)=2×3-5>0$
$∴f(3)=2×27-15×9+36×3+1=24$
(C) $f(x)=\frac{x}{2}-x^2$
for max. value $f'(c)=0$
$⇒\frac{1}{2}-2x=0$
$⇒x=\frac{1}{4}$
$∴f(\frac{1}{4})=\frac{1}{8}-\frac{1}{16}=\frac{1}{16}$
(D) $f(x)=\frac{9}{(x+3)}+x$
for min. value $f'(c)=0$
$⇒\frac{-9}{(x+3)^2}+1=0$
$⇒(x+3)^2=9$
$⇒x+3=3$ or $x+3=-3$
$⇒x=0$, $x=-6$
$f(-6)=\frac{9}{-6+3}+(-6)$
$=\frac{9}{-3}+(-6)$
$=-9=\frac{-36}{4}$