Toán Lớp 7: Yìm x biết: a, 3^x-1+5.3^x-1=162 b. 3x+x^2=0

Question

Toán Lớp 7:  Yìm x biết:  a, 3^x-1+5.3^x-1=162  b. 3x+x^2=0

hoaiphuong85 · Answer

Lời giải chi tiết:     a) 3^(x-1)+5xx3^(x-1)=162   =>3^(x-1)xx(1+5)=162   =>3^(x-1)xx6=162   =>3^(x-1)=162:6   =>3^(x-1)=27   =>3^(x-1)=3^3   =>x-1=3   =>x=3+1   =>x=4   Vậy x=4   b) 3x+x^2=0   =>3x+xxxx=0   =>xxx(3+x)=0   => ( left[  begin{array}{l}x=0  3+x=0 end{array}  right. )   => ( left[  begin{array}{l}x=0  x=-3 end{array}  right. )   Vậy x=0 hoặc x=-3                                                      @uniquetimehunter

diemchau · Answer

a) 3^(x-1) + 5 xx 3^(x-1) = 162 $ $ <=> 3^(x-1) xx (1+5) = 162 $ $ <=> 3^(x-1) xx 6 = 162 $ $ <=> 3^(x-1) = 162 : 6 $ $ <=> 3^(x-1) = 27 $ $ <=> 3^(x-1) = 3^3 $ $ <=> x - 1 = 3 $ $ <=> x = 3 + 1 $ $ <=> x = 4 $ $ text{Vậy, } x = 4 ---------------------------------------- b) 3x + x^2 = 0 $ $ <=> 3x + x xx x = 0 $ $ <=> x xx (3 + x) = 0 $ $ <=> ( left[ begin{array}{l}x=0 3+x=0 end{array} right. ) $ $ <=> ( left[ begin{array}{l}x=0 x=-3 end{array} right. ) $ $ text{Vậy, } x in {0 ; -3}