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secondary 4 | A Maths
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Chelsea
Chelsea

secondary 4 chevron_right A Maths chevron_right Singapore

Pls help for q1 & q2!

Date Posted: 1 month ago
Views: 12
snell
Snell
1 month ago
1.
let X be 3ˣ

9ˣ - 15(3ˣ⁻¹) - 14 = 0
3²ˣ - 15(3ˣ/3) - 14 = 0
(3ˣ)² - 5(3ˣ) - 14 = 0
X² - 5X - 14 = 0
(X-7)(X+2) = 0
X = 7 or X = -2

subst. X = 3ˣ ,
3ˣ = 7 or 3ˣ = -2 (n.a.)
x = lg 7/lg 3
= 1.77


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