Algebra Question - Topic

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Aug 2 2013 03:18pm

f is an exponential function defined by f(x) = pr^x, where p and r are positive constants. If f(2) = 48 and f(4) = 768, what is the value of p?

This post was edited by saviorzx on Aug 2 2013 03:19pm

Azrad

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Aug 2 2013 03:55pm

f(2) = 48 = p*r^2
f(2) = 48 = p*b, b=r^2
f(4) = 768 = p*b^2

eq#1--> 48 = p*b
eq#2--> 768 = p*b^2

eq#1--> b= 48/p
sub that into eq#2:

eq#2-->768 = p*(48/p)^2
eq#2-->768 = p*(2304/p^2)
eq#2-->768 = 2304/p
eq#2-->p = 2304/768
eq#2-->p = 3

problem did not ask for r, but here it is:
sub that into first line
48 = 3*r^2
16 = r^2
r= +/- 4

This post was edited by Azrad on Aug 2 2013 03:56pm

saviorzx

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Aug 2 2013 03:56pm

Quote (Azrad @ Aug 2 2013 05:55pm)

f(2) = 48 = p*r^2
f(2) = 48 = p*b, b=r^2
f(4) = 768 = p*b^2

eq#1--> 48 = p*b
eq#2--> 768 = p*b^2

eq#1--> b= 48/p
sub that into eq#2:

eq#2-->768 = p*(48/p)^2
eq#2-->768 = p*(2304/p^2)
eq#2-->768 = 2304/p
eq#2-->p = 2304/768
eq#2-->p = 3

problem did not ask for r, but here it is:
sub that into first line
48 = 3*r^2
16 = r^2
r= +/- 4

thanks

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