indices

[normal sun]

i made a subsitution and made it a quadratic

so like 9y^2-30y+81= 0

i got y = 27 y = 3

so then 27 = 9^x-1 and 3 = 9^x-1

but dont know where to go from there

[hushed ore]

u just solve for x

9^(x-1) = 27
ln(9^x-1) = ln27

(x-1)ln(9) = ln27

xln9 - ln9 = ln27

xln9 = ln 27 + ln 9
xln9 = ln(27 x 9)
x = ln(27x9)/ln9

simplify the rhs a bit more and yh

[normal sun]

ive never used ln not been taught

so i got no clue

[hushed ore]

using ln is no different to using log base 10

have you done logs at all?

[normal sun]

nope

only got up to pure topic 10

so far

[hushed ore]

wheres logs

ch 11?

[normal sun]

i think ch 14

[hushed ore]

oh

we could solve it using indices then

9^(x-1) = 27
1/9 * 9^x = 27
9^x = 243
3^(2x) = 243
3^(2x) = 3^5
2x = 5
x = 2.5

[normal sun]

yep that will make more sense

ok that makes sense thankss!