Quantitative Aptitude Ques 324
Question: The value of $ {{\sec }^{4}}A,(1-{{\sin }^{4}}A)-2{{\tan }^{2}}A $ is
Options:
A) $ \frac{1}{2} $
B) 1
C) 0
D) 2
Show Answer
Answer:
Correct Answer: B
Solution:
- $ {{\sec }^{4}}A,(1-{{\sin }^{4}}A)-2{{\tan }^{2}}A $
$ ={{\sec }^{4}}A,[(1-{{\sin }^{2}}A)[(1+{{\sin }^{2}}A)]-2tan^{2}A $
$ ={{\sec }^{4}}\cdot cos^{2}A(1+{{\sin }^{2}}A)-2tan^{2}A $
$ [\because 1-{{\sin }^{2}}A={{\cos }^{2}}A] $
$ ={{\sec }^{2}}A+,(1+{{\sin }^{2}}A)-2tan^{2}A $
$ ={{\sec }^{2}}A+{{\sec }^{2}}A{{\sin }^{2}}A-2{{\tan }^{2}}A $
$ =1+tan^{2}A+\frac{{{\sin }^{2}}A}{{{\cos }^{2}}A}-2{{\tan }^{2}}A $
$ =1-{{\tan }^{2}}A+{{\tan }^{2}}A=1 $