Question

7^2x+2.7^x - 15 =0 please solve it?

Answer 1

let 7^x = a

=> 7^2x+2.7^x - 15 =0= a²+2a-15

=> a²+2a-15 =0

=> a²+5a-3a-15 = 0

=> a(a+5)-3(a+5)= 0

=> (a-3)(a+5)=0

=> a = 3 or a = -5

=> 7^x = 3 or 7^x = -5

=> log 7 base 3 = x or

log7 base-5 = x (not possible )