Question

a la patrat - b la patrat= 45
a + b= 15
5a - 5b= ?

Answer 1

a² - b²= 45
(a+b)(a-b)=45
a + b= 15 
15(a-b)=45
a-b= 3
5a - 5b= 5(a-b)=5×3=15

Answer 2

$a^2-b^2 = 45 =\ \textgreater \ (a-b)(a+b) = 45$;
Fiindca avem pe a+b = 15, obtinem:
$15(a-b)=45=\ \textgreater \ a-b=3$;
5a - 5b = 5(a-b) = 5 * 3 = 15.
Mult succes in continuare!