c)

 \(x^2-y^2+3x-3y\\ =\left(x+y\right)\left(x-y\right)+3\left(x-y\right)\\ =\left(x-y\right)\left[\left(x+y\right)+3\right]\)

d)

\(x^3+3x^2-16x-48\\ =x\left(x^2-16\right)+3\left(x^2-16\right)\\ =\left(x^2-16\right)\left(x+3\right)\\ =\left(x+4\right)\left(x-4\right)\left(x+3\right)\)

C

1) Ta có A khi x = 49 :

\(A=\dfrac{7}{3\sqrt{49}}=\dfrac{7}{21}=\dfrac{1}{3}\)

Vậy khi x = 49 thì \(A=\dfrac{1}{3}\)

2) 

\(B=\dfrac{\sqrt{x}}{\sqrt{x}-1}+\dfrac{2\sqrt{x}-8}{3x-3}\left(x\ge0;x\ne1\right)\\ =\dfrac{\sqrt{x}}{\sqrt{x}-1}+\dfrac{2\sqrt{x}-8}{3\left(x-1\right)}\\ =\dfrac{3\sqrt{x}\left(\sqrt{x}+1\right)+2\sqrt{x}-8}{3\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\\ =\dfrac{3x+3\sqrt{x}+2\sqrt{x}-8}{3\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\\ =\dfrac{3x+5\sqrt{x}-8}{3\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\\ =\dfrac{3\sqrt{x}+8}{3\left(\sqrt{x}+1\right)}\)

chắc thế :/

tặng kính cho bạn :)))

Hàm số y = ax + b đồng biến khi nào nghịch biến khi nào ?

xin lỗi nhưng mình ko làm đc :((