Question

if a^2-b^2=15 and (a-b)=7 what is the value of(a+b)

Answer 1

$\bf \textit{difference of squares} \\\\ (a-b)(a+b) = a^2-b^2 \\\\[-0.35em] ~\dotfill\\\\ a^2-b^2=15\implies (a-b)(a+b)=15\implies \stackrel{\stackrel{a-b}{\downarrow }}{(7)}(a+b)=15\implies a+b=\cfrac{15}{7}$