Răspuns :
Folosim formula:
(a + b)² - a² - b² = a² + 2ab + b² - a² - b² = 2ab
=> (7/5 + 3/5)²- (7/5)²-(3/5)² = 2 * (7/5) * (3/5) = 42 / 25
(a + b)² - a² - b² = a² + 2ab + b² - a² - b² = 2ab
=> (7/5 + 3/5)²- (7/5)²-(3/5)² = 2 * (7/5) * (3/5) = 42 / 25