If $f (x) = \sqrt{x}$ $f(x)=sqrtx$ , $g (x) = 7 x + b$ $g(x)=7x+b$ and $f (g (x))$ $f(g(x))$ passes through $(4, 6)$ $(4,6)$ , what is $b$ $b$ ?

Question

A $8$ $8$
B $26$ $26$
C $6$ $6$
D $4$ $4$

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Answer 1 · 2017-03-17T06:22:36

Answer is A.

As $f (x) = \sqrt{x}$ $f(x)=sqrtx$ and $g (x) = 7 x + b$ $g(x)=7x+b$ .

$y = f {g (x)} = \sqrt{7 x + b}$ $y=f{g(x)}=sqrt(7x+b)$

As it passes through $(4, 6)$ $(4, 6)$

$6 = \sqrt{7 \times 4 + b}$ $6=sqrt(7xx4+b)$ and squaring both sides, we get

$36 = 28 + b$ $36=28+b$

or $b = 36 - 28 = 8$ $b=36-28=8$

Hence, answer is A.