Question

Given that f(x) = √(ax + 1) , with x ≥ -1/a and a > 0

Answer 1

Answer:

$\displaystyle 7$

Step-by-step explanation:

first thing I assume by f~¹ you meant $f^{-1}$ however

we want to find a²+3x-3 for the given condition. with the composite function condition we can do so

Finding the inverse of f(x):

$\displaystyle f(x) = \sqrt{ax + 1}$

substitute y for f(x):

$\displaystyle y= \sqrt{ax + 1}$

interchange:

$\displaystyle x= \sqrt{ay + 1}$

square both sides:

$\displaystyle ay + 1 = {x}^{2}$

cancel 1 from both sides:

$\displaystyle ay = {x}^{2} - 1$

divide both sides by a:

$\displaystyle y = \frac{{x}^{2} - 1 }{a}$

substitute f^-1 for y:

$\displaystyle f ^{ - 1} (x) = \frac{{x}^{2} - 1 }{a}$

finding the inverse of g(x):

$\displaystyle g(x) = \frac{x + 1}{x}$

substitute y for g(x)

$\displaystyle y= \frac{x + 1}{x}$

interchange:

$\displaystyle \frac{y + 1}{y} =x$

cross multiplication

$\displaystyle y + 1= xy$

cancel 1 from both sides

$\displaystyle y - xy= - 1$

factor out y:

$\displaystyle y(1 - x)= - 1$

divide both sides by 1-x:

$\displaystyle y= - \frac{1}{ 1 - x}$

substitute g^-1 for y:

$\displaystyle g ^{ - 1} (x)= - \frac{1}{ 1 - x}$

remember that

$\displaystyle (f \circ g)x = f(g(x))$

therefore we obtain:

$\rm \displaystyle (f ^{ - 1} \circ g ^{ - 1} ) (3) = \frac{{ \bigg(- \dfrac{1}{1 - 3} } \bigg)^{2} - 1 }{a}$

since (f~¹•g~¹)(3)=-⅜ thus substitute:

$\rm \displaystyle \frac{{ \bigg(- \dfrac{1}{1 - 3} } \bigg)^{2} - 1 }{a} = - \frac{3}{8}$

simplify parentheses:

$\rm \displaystyle \frac{{ \bigg( \dfrac{1}{2} } \bigg)^{2} - 1 }{a} = - \frac{3}{8}$

simplify square:

$\rm \displaystyle \frac{{ \dfrac{1}{4} } - 1 }{a} = - \frac{3}{8}$

simplify substraction:

$\rm \displaystyle \frac{ - \dfrac{3}{4} }{ a}= - \frac{3}{8}$

simplify complex fraction:

$\rm \displaystyle - \dfrac{3}{4a} = - \frac{3}{8}$

get rid of - sign:

$\rm \displaystyle \dfrac{3}{4a} = \frac{3}{8}$

divide both sides by 3:

$\rm \displaystyle \dfrac{1}{4a} = \frac{1}{8}$

cross multiplication:

$\rm \displaystyle 4a= 8$

divide both sides by 4:

$\rm \displaystyle \boxed{ a= 2}$

as we want to find a²+3a-3 substitute the got value of a:

$\displaystyle {2}^{2} + 3.2 - 3$

simplify square:

$\displaystyle 4 + 3.2 - 3$

simplify multiplication:

$\displaystyle 4 +6 - 3$

simplify addition:

$\displaystyle 10 - 3$

simplify substraction:

$\displaystyle 7$

and we are done!