If $49a^2 + 25b^2 = 30$ and ab = 1, b > 0, then the value of (7a + 5b) is :

14 8 12 10

10

We know, If, x2 + y2 = b and x + y = \(\sqrt {b + 2xy}\) If $49a^2 + 25b^2 = 30$ ab = 1, b > 0, then the value of (7a + 5b) = \(\sqrt {30 + 2 × 7 × 5}\) = \(\sqrt {100}\) = 10