Toán Lớp 7: Tìm `n`: `a)9.27^n=3^5` `b)(2^3:4).2^n=4` `c)3^(-2).3^4.3^n=3^7` `d)2^(-1).2^n+4.2^n=9.2^5`

Question

Toán Lớp 7:  Tìm n: a)9.27^n=3^5 b)(2^3:4).2^n=4 c)3^(-2).3^4.3^n=3^7 d)2^(-1).2^n+4.2^n=9.2^5

huenthanh97 · Answer

a, 3^2 . 3^(3.n) = 3^5     &hArr; 2 + ( 3 . n ) = 5     &hArr; 3 . n = 3     &hArr; n = 1     Vậy n = 1     b, ( 2^3 : 4 ) . 2^n = 4     &hArr; ( 2^3 : 2^2 ) . 2^n = 2^2     &hArr; ( 3 - 1 ) . n = 2     &hArr; 2 . n = 2     &hArr; n = 1     Vậy n = 1     c, 3^(-2) . 3^4 . 3^n = 3^7     &hArr; -2 + 4 + n = 7     &hArr; 2 + n = 7     &hArr; n = 5     Vậy n = 5     d, 2^(-1) . 2^n + 4 . 2^n = 9 . 2^5     &hArr; 2^(-1) + 2^n + 2^2 . 2^n = 9 . 2^5     &hArr; 2^n . 9/2 = 9 . 2^5     &hArr; 2^n . 1 = 2^6     &hArr; n = 6     Vậy n = 6

tuyethutanhthu · Answer

a)9.27^n=3^5 <=>3^2 .27^n=3^5 <=>27^n=3^3 <=>27^n=27 <=>n=1 Vậy n=1 b)(2^3:4).2^n=4 <=>(2^3:2^2).2^n=4 <=>2.2^n=4 <=>2^n=2 <=>n=1 Vậy n=1 c)3^-2 .3^4 .3^n=3^7 <=>3^2. 3^n=3^7 <=>3^n=3^5 <=>n=5 Vậy n=5 d)2^-1 .2^n+4.2^n=9.2^5 <=>2^n(2^-1+4)=9.2^5 <=>2^n. 9/2=9.2^5 <=>2^n=2^6 <=>n=6 Vậy n=6