Question

[Sagittarus]

chứng minh rằng nếu \(\frac{a}{b}=\frac{c}{d}\)

thì :\(\frac{7a^2+3ab}{11a^2-8b^2}=\frac{7c^2+3cd}{11c^2-8d^2}\)

Answer 1

[Trần Tuyết Như]

a/b = c/d           => a/c = b/d 

=> a² / c² = b² / d²  = ab / cd

<=> 7a² / 7c² = 11a² / 11c²  = 8b² / 8d² = 3ab / 3cd

=> 7a² + 3ab / 7c² + 3cd = 11a² - 8b² / 11c² - 8d²

=> 7a² + 3ab / 11a² - 8b² = 7c² + 3cd / 11c² - 8d²                (đpcm)