If 2a + 5b = 12 and ab = 3, find the value of 4a2 + 25b2.
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 84.
2a + 5b = 12
Squaring both sides, we get
⇒ 4a2 + 25b2 + 20ab = 144
We have ab = 3
Thus, 4a2 + 25b2 + 60 = 144
and, 4a2 + 25b2 = 84