Quantitative Aptitude Ques 1800
Question: If $ 3x+2y=12 $ and $ xy=6, $ then the value of $ 9x^{2}+4y^{2} $ is
Options:
A) 76
B) 80
C) 72
D) 74
Show Answer
Answer:
Correct Answer: C
Solution:
- Given, equations are $ 3x+2y=12 $ (i) $ xy=6 $ (ii) On squaring Eq. (i) on both sides, we get $ {{(3x+2y)}^{2}}={{(12)}^{2}} $
$ \Rightarrow $ $ 9x^{2}+4y^{2}+12xy=144 $
$ \Rightarrow $ $ 9x^{2}+4y^{2}=144-12xy $
$ \Rightarrow $ $ 9x^{2}+4y^{2}=144-12(6) $ [From Eq. (ii)]
$ \Rightarrow $ $ 9x^{2}+4y^{2}=144-72=72 $
BETA
