If 7b - (1/4b) = 7, then what is the value of 16b2 + (1/49b2) ?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is Option 3 i.e. 120/7.
7b - 1/4b = 7
multiply both sides by 4/7
⇒ 7 × 4/7b - 1/4 × 4/7b = 7 × 4/7
⇒ 4b - 1/7b = 4
Now, squaring both sides
⇒ (4b - 1/7b)2 = 16
⇒ 16 b2 + 1/49 b2 - 2 × 4b × 1/7b = 16
⇒ 16b2 + 1/49b2 - 2 × 4/7 = 16
⇒ 16b2 + 1/49b2 = 16 + 8/7
⇒ 16b2 + 1/49b2 = 120/7