Giải câu 1 trang 43 sách VNEN toán 8 tập 1.

a)  $\frac{5}{x^{5}y^{3}}$; $\frac{7}{12x^{3}y^{4}}$

Ta có: $\frac{5}{x^{5}y^{3}}=\frac{5}{x^{2}y.x^{3}y^{3}}$

$\frac{7}{12x^{3}y^{4}}=\frac{7}{12y.x^{3}y^{3}}$

MTC là $12x^{5}y^{4}$

Suy ra: $\frac{5}{x^{5}y^{3}}=\frac{5.12y}{12x^{5}y^{4}}=\frac{60y}{12x^{5}y^{4}}$

$\frac{7}{12x^{3}y^{4}}=\frac{7}{12y.x^{3}y^{3}}=\frac{7x^{2}}{12x^{5}y^{4}}$

b) $\frac{4}{15x^{3}y^{5}}$; $\frac{11}{12x^{4}y^{2}}$

Ta có: 

$\frac{4}{15x^{3}y^{5}}=\frac{4}{3x^{3}y^{2}.5y^{3}}$

$\frac{11}{12x^{4}y^{2}}=\frac{11}{3x^{3}y^{2}.4x}$

MTC là $3x^{3}y^{2}.20xy^{3}=60x^{4}y^{5}$

Suy ra: 

$\frac{4}{15x^{3}y^{5}}=\frac{16x}{60x^{4}y^{5}}$

$\frac{11}{12x^{4}y^{2}}=\frac{55y^{3}}{60x^{4}y^{5}}$