How do you solve 62^(x+3) <= 7^(2x+1)62x+372x+1?

2 Answers
Mar 19, 2016

take the common logarithm of both sides and you will get:

log62^(x+3)<=log7^(2x+1)log62x+3log72x+1

using the power rule for logs, the exponents become factors or multipliers and the equation reduces to:

(x+3)log62<=(2x+1)log7(x+3)log62(2x+1)log7
by expanding , we will obtain a simple linear equation with 1 variable (x):

xlog62 + 3log62 <= 2xlog7 + 1log7

collect all your x terms on one side of the equation and the others on the opposite side:

xlog62 - 2xlog7 <= log7 - 3log62

factoring the common factor of 'x':

x(log62 - 2log7) <= log7 - 3log62

and the result is:

x <= (log7-3log62)/(log62-2log7)log73log62log622log7

Mar 19, 2016

x" ">=" " (ln(7^5))/(ln(7^2/62))-3x ln(75)ln(7262)3

If you prefer: x" ">=" " (5ln(7))/(2ln(7)-ln(62)) -3x 5ln(7)2ln(7)ln(62)3

Explanation:

You could use any form of log for this. I chose log_eloge

Taking logs of both sides

" "(x+3)ln(62)color(red)(<=)(2x+1)ln(7) (x+3)ln(62)(2x+1)ln(7)

" "=>(ln(62))/(ln(7))color(red)(<=)(2x+1)/(x+3) ln(62)ln(7)2x+1x+3

Dividing the right hand side gives

" "(ln(62))/(ln(7))color(red)(<=)2 -5/(x+3) ln(62)ln(7)25x+3

" "(ln(62))/(ln(7))-2color(red)(<=) -5/(x+3) ln(62)ln(7)25x+3

Multiply by (-1)

" "2-(ln(62))/(ln(7))color(red)(>=) +5/(x+3) 2ln(62)ln(7)+5x+3

" "(x+3)(2-(ln(62))/(ln(7)))color(red)(>=) +5 (x+3)(2ln(62)ln(7))+5

" "x+3 color(red)(>=) 5 xx (ln(7))/(2ln(7)-ln(62)) x+35×ln(7)2ln(7)ln(62)

" "xcolor(red)(>=) (5ln(7))/(2ln(7)-ln(62)) -3 x5ln(7)2ln(7)ln(62)3

" "xcolor(red)(>=) (ln(7^5))/(ln(7^2/62))-3 xln(75)ln(7262)3