Find the mean proportional of (12 + 6) and (8 − 4).
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 4.
Mean proportional between a and b = √(a × b)
a = 12 + 6√2 , b = 8 − 4√2
(12 + 6√2)(8 − 4√2)
= 12×8 − 12×4√2 + 6√2×8 − 6√2×4√2
= 96 − 48√2 + 48√2 − 48
= 96 − 48 = 48
√(48) = √(16 × 3) = 4√3