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5. Continuity and Differentiation
normal
Mean value theorem $f(b) -f(a) = (b -a) f '(x_1);$ from $a < x_1 < b,$ if $f(x) = 1/x$ then $x_1 = ?$
A
$\sqrt {ab}$
B
$\frac{{2ab}}{{a + b}}$
C
$\frac{{a + b}}{{2}}$
D
$\frac{{b - a}}{{b + a}}$
Solution
$f^{\prime}(x)=\frac{f(b)-f(a)}{b-a}$
$\frac{-1}{x^{2}}=\frac{\frac{1}{b}-\frac{1}{a}}{b-a}$
$\frac{{ – 1}}{{{x^2}}} = \frac{{a – b}}{{ab(b – a)}}$
$\frac{1}{x^{2}}=\frac{1}{a b}$
Standard 12
Mathematics