Question

binary

17跟20題應該怎麼解

Answer 1

S

20題
(7^x)^2+5*7x-24=0
設7^x=t
t^2+5t-24=0
(t-3)(t+8)=0
t=3 (-8不合)
7^(x+1)=7^x*7=3*7=21

17題
3^(x+2)-3^x=24√3
9*3^x-3^x=24√3
8*3^x=24√3
3^x=3√3
x=3/2