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5. Continuity and Differentiation
hard
Consider the function $f (x) = 8x^2 - 7x + 5$ on the interval $[-6, 6]$. The value of $c$ that satisfies the conclusion of the mean value theorem, is
A
$- 7/8$
B
$-4$
C
$7/8$
D
$0$
Solution
$f ' (c) = 16c – 7 = \frac{{f(6) – f( – 6)}}{{12}}$
$=\frac{{(8\,\cdot\,36 – 7\,\cdot\,6 + 5) – (8.36 + 7.6 + 5)}}{{12}} $
$= -\frac{{2\,\cdot\,7\,\cdot\,6}}{{12}} = – 7$
$16c = 0\,==>\,c = 0$
Standard 12
Mathematics