Toán Lớp 8: Bài 5.Tìm x ( sử dụng công thức A.B=0 suy ra A=0 hay B=0 2) A^n=0 suy ra A=0 ) a)x^2-16=0 b) x^2 +10x+25=0 c) x^2-4=0

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Toán Lớp 8:  Bài 5.Tìm x ( sử dụng công thức A.B=0 suy ra A=0 hay B=0 2) A^n=0 suy ra A=0 ) a)x^2-16=0         b) x^2 +10x+25=0        c) x^2-4=0     d)36-x^2=0 e) 1-25x^2=0      f)x^2-x+1/4=0               g) 25-10x+x^2= 0

catlantuong · Answer

~ gửi bạn ~   Giải đáp:   a) $ left[ begin{matrix} x = 4   x = - 4 end{matrix} right.$   b)  x = -5   c) $ left[ begin{matrix} x = 2   x = - 2 end{matrix} right.$   d) $ left[ begin{matrix} x = 6   x = - 6 end{matrix} right.$   e) $ left[ begin{matrix} x =  dfrac{1}{5}   x =  dfrac{-1}{5} end{matrix} right.$   f)  x = 1/2   g)  x = 5   Lời giải và giải thích chi tiết:   a) x^2 - 16 = 0   &hArr; x^2 - 4^2 = 0   &hArr;(x - 4)*(x + 4) = 0   &hArr; $ left[ begin{matrix} x+4=0   x-4=0 end{matrix} right.$   &hArr; $ left[ begin{matrix} x = 4   x = - 4 end{matrix} right.$   -----------------   b) x^2 + 10x + 25 = 0   &hArr; x^2 + 2*x*5 + 5^2 = 0   &hArr; (x + 5)^2 = 0   &hArr; x = -5   ------------------   c) x^2 - 4 = 0   &hArr; x^2 - 2^2 = 0   &hArr; (x - 2)*(x + 2) = 0   &hArr; $ left[ begin{matrix} x+2=0   x-2=0 end{matrix} right.$   &hArr; $ left[ begin{matrix} x = 2   x = - 2 end{matrix} right.$   -------------------   d) 36 - x^2 = 0   &hArr; 6^2 - x^2 = 0   &hArr; (6 - x)*(6 + x) = 0   &hArr; $ left[ begin{matrix} 6 - x = 0   6 + x = 0 end{matrix} right.$   &hArr; $ left[ begin{matrix} x = 6   x = - 6 end{matrix} right.$   --------------------   e) 1 - 25x^2 = 0   &hArr; 1 - (5x)^2 = 0   &hArr; (1 - 5x)*(1 + 5x) = 0   &hArr; $ left[ begin{matrix} 1 - 5x = 0   1 + 5x= 0 end{matrix} right.$   &hArr; $ left[ begin{matrix} x =  dfrac{1}{5}   x =  dfrac{-1}{5} end{matrix} right.$   ---------------------   f) x^2 - x + 1/4 = 0   &hArr; x^2 - 2*x* 1/2 + 1/4 = 0   &hArr; (x - 1/2)^2 = 0   &hArr; x = 1/2   -----------------------   g) 25 - 10x + x^2 = 0   &hArr; x^2 - 10x + 25 = 0   &hArr; x^2 - 2*x*5 + 5^2 = 0   &hArr; (x - 5)^2 = 0   &hArr; x = 5

thaolanphuobg · Answer

Giải đáp+Lời giải và giải thích chi tiết:   $a) x^2 -16 =0$    x^2 -4^2 =0     (x-4)(x+4)     $ left[ begin{matrix} x-4=0   x+4=0 end{matrix} right.$     $ left[ begin{matrix} x=4   x=-4 end{matrix} right.$     b) x^2 +10x+25=0     x^2 +2.x.5 +5^2 =0     (x+5)^2 =0     x+5=0     x=-5     c) x^2-4=0      x^2 -2^2 =0     (x-2)(x+2)=0    $ left[ begin{matrix} x-2=0   x+2=0 end{matrix} right.$   $ left[ begin{matrix} x=2   x=-2 end{matrix} right.$   d)36-x^2 =0   6^2 -x^2 =0   (6-x)(6+x)=0   $ left[ begin{matrix} 6-x=0   6+x=0 end{matrix} right.$   $ left[ begin{matrix} x=6   x=-6 end{matrix} right.$   e)1-25x^2 =0   1^2 -(5x)^2 =0   (1-5x)(1+5x)=0   $ left[ begin{matrix} 1-5x=0   1+5x=0 end{matrix} right.$   $ left[ begin{matrix} x=1/5   x=-1/5 end{matrix} right.$   f)x^2 -x+1/4 =0   x^2 -2.x. 1/2 +(1/2)^2 =0   (x- 1/2)^2 =0   x- 1/2 =0   x=1/2   g)25-10x+x^2 =0   5^2 -2.5.x +x^2 =0   (5-x)^2=0   5-x=0   x=5