Toán Lớp 7: Cho hàm số y=f(x)=x mũ 2 + 5 a) Tính f(2); f(-1/3) b) Tìm x để f(x) = x+5

Question

Toán Lớp 7:  Cho hàm số y=f(x)=x mũ 2 + 5 a) Tính f(2); f(-1/3)  b) Tìm x để f(x) = x+5

ngoclandiep · Answer

$ text{a) Ta c&oacute;:}$        $f(x)=x^2+5$   &rArr; $f(2)=2^2+5=9$   &rArr; $f left(- dfrac{1}{3} right)= left(- dfrac{1}{3} right)^2+5= dfrac{46}{9}$   $ text{}$   $ text{b) Ta c&oacute;:}$        $f(x)=x+5$   &hArr; $x^2+5=x+5$   &hArr; $x^2-x=0$   &hArr; $x(x-1)=0$   &hArr; $ left[ begin{array}{l}x=0  x-1=0 end{array} right.$   &hArr; $ left[ begin{array}{l}x=0  x=1 end{array} right.$

hauthanhyen98 · Answer

Answer    $ text{a, Ta c&oacute;:}$ y = f(x) = x^2 + 5   $ text{V&oacute;i}$ f(2)   => 2^2 + 5   = 4 + 5   = 9   $ text{Với}$ f(-1/3)   => (-1/3)^{2} + 5   = 1/9 + 5   = 46/9   ______________________   $ text{b, Ta c&oacute;}$ y = f(x) = x^2 + 5   => x^2 + 5 = x + 5   => x^2 + 5 - x - 5 = 0   => x^2 - x + 5 - 5 = 0   => x^2 - x = 0   => x . (x - 1) = 0   => $ left[ begin{matrix} x = 0   x - 1 = 0 end{matrix} right.$   => $ left[ begin{matrix} x = 0   x = 0 + 1 end{matrix} right.$   => $ left[ begin{matrix} x = 0   x = 1 end{matrix} right.$   $ text{Vậy}$ x  in {0 ; 1}