$\mathrm{ExOO}^{3}$ \[ \left\{\begin{array}{l} a^{2}-b^{2}=400 \\ a-b=10 \end{array}\right. \] (2) Determinier les reels $a$ et $b$ ?

Step 1 ：Solve the second equation for a: \(a = b + 10\)

Step 2 ：Substitute the expression for a into the first equation: \((b + 10)^2 - b^2 = 400\)

Step 3 ：Solve the equation for b: \(b = 15\)

Step 4 ：Find the value of a: \(a = 15 + 10 = 25\)

Step 5 ：\(\boxed{a = 25, b = 15}\)