If a + 5b = 13 and ab = 9, find the value of a2 + 25b2.
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 79.
a + 5b = 13
⇒ (a + 5b)2 = 132
⇒ a2 + 2(a)(5b) + (5b)2 = 169
⇒ a2 + 10ab + 25b2 = 169
⇒ a2 + 10(9) + 25b2 = 169
⇒ a2 + 25b2 = 169 - 90 = 79
Therefore, the value of a2 + 25b2 is 79.