Question

柔柔

這題怎麼解

19. 若 272x+12=34x(x-1),且x>0,則2x+12=?
(A) 27
(B) 21
2x+12
(C) 8
3270+12
(3)
=
2
3
(D) 6
4x²-40
201
10 +12)²
198

Answer 1

kevin_maphy

27^(2x+12)=3^(4x(x-1))
(3^3)^(2x+12)=3^(4x(x-1))
3^(6x+36)=3^(4x^2-4x)

因此6x+36=4x^2-4x
4x^2-10x-36=0
2x^2-5x-18=0
(2x-9)(x+2)=0
x=9/2或-2(-2不合)

2x+12=9+12=21

答案為(B)